why do people like Decade?

[ShinkenW]

Sentai is different to KR, it's more difficult for them to bring back the original actors from KR than it is to get those from Sentai back.

Here is the reason...in Sentai, we have a team of at least 5 senshis in each season...for Gokaiger, at the very least, Toei only needed to bring back just ONE actor/actress who had originally portrayed a member on each Sentai team, it would not matter which senshi they brought back, because they all belonged to the same Sentai teams...so any actor they brought back who had portrayed a senshi from those Sentai teams would be enough to serve their purpose in the tributes in Gokaiger.

But with KR, each season only has 1 protagonist, 1 main Rider, and he is the namesake for each season...although W has 2 protagonists because of its 2-in-1 Rider concept, but W came out after Decade so it is excluded in this case.
Anyway, when they made Decade with the intent on focusing on the previous KR seasons, if the arcs were to revolve around the original characters, then Toei would have needed to at least bring back all those actors who had originally portrayed those main Riders specifically in the original seasons, that was a must. And I know for a fact that some of those actors were very busy with other works and are hard to bring back, such as Odagiri Joe who played the original Kuuga, Mizushima Hiro (Kabuto) was working nonstop since Kabuto, Kashu Toshiki (Agito) was busy filming a drama at the time, and Sato Takeru (Den-O) as been working endlessly since the end of the Den-O series.
Even some of the actors who had played the secondary Riders and non-Rider characters in those seasons were busy with other works too.

If Toei had tried to bring back as many original actors as they could and have the writers try to write the arcs with the original characters they have on hand...it would have been quite messy & nonsensical story wise, considering most of those original actors they could bring back, wouldn't even be the main casts from the original seasons. But then again, if the arcs were to have the original main actors, but completely different supporting casts, then the arcs probably wouldn't have made much sense either.
So it's much easier for the writers to just start from scratch & write the arcs in alternate settings to the original seasons and cast new actors for new characters replacing the originals. As oppose to

What I don't understand is that they were able to bring back both Seto Koji and Tsubaki Takayuki...so why were the Kiva and Blade arcs set in alternate worlds instead of the original worlds?

[Mr. CD]

And yet, they were able to get almost the entire casts of Den-O and Hibiki back for their episodes. And, early on in the series, they were able to get Hidenori Tokuyama, Masato Uchiyama, and Kohei Murakami back to voice KickHopper, PunchHopper, and Kaixa respectively. I still not buying it would have been hard to get any of the original actors back. Heck, quite a few of them weren't doing anything big at the time. The whole AU thing seems like an excuse to not try to get anyone back. Hell, you could still do AUs even with the original cast (dopplegangers anyone?).

[Captain Platypus]

Plus, I'm sorry; getting old actors back is meaningless to me. I don't get exited to see the same old faces and the same old characters. This fandom is so intent on old characters coming back and that somehow makes a series awesome that they're not worried about the story. They're willing to fall for a gimmick instead of something that matters

[Mr. CD]

No, it's not that people think bringing back old characters makes a show automatically better, it's just that it's pointless to make a big anniversary celebrations about honoring the past and all that, NOT bring anybody back. if Decade was merely just a normal Rider series with a quick note saying that this is the anniversary, like Agito and Kabuto did, it wouldn't be a problem, but since they went through all the trouble of repairing and recreating all of the old suits, it seems pointless to do that without bringing anybody back. Who cares about seeing a bunch of old suits slugging it out? We can see that in any Tokyo Domeshow. Getting the face behind the mask, that's what makes it all the more special seeing the suits back.

[Digifiend]

The story was complex? I will quote Wataru here, from Movie Wars 2010; "Decade has no story."

That line was said a few times. In truth, it was really Natsumi's story. She starts off as a normal girl who has nightmares about Decade. In the end, the nightmare comes true, so she becomes a Rider herself, Kamen Rider Kivara, and kills him. That was a major piece of character development, and although Kivara was a movie-exclusive Rider, it was also Natsumi's last appearance, so she was never shown to lose the powers. After Decade's resurrection, they must've gone their separate ways, since she's absent from Super Hero Taisen (and Kuuga in that film is presumably the original instead of the AR version).

[Koji]

As a massive Hibiki fan, even getting the original cast back for Hibiki's World wasn't that great for me. I loved seeing them; don't get me wrong, but the lack of Hibiki himself and Asumu piss me off. That, and sure, it's an AU, but the Oni system. Asumu was Kyoki, then he becomes Hibiki. That's not how it works. Did Akira become Ibuki? No. Did...crap, can't think of his name, become Zanki? No. Amaki and Todoroki.

But Decade overall is a mess. It's painful to watch. Utterly painful. Den-O painful (I despise Den-O with a passion, an unrivaled passion). The only good thing about the AU is it didn't pull a Gokaiger and push everything into one backstory. It would have been interesting to see Decade make it all into one, but a mess in the end. I guess the AU is good for that case, at the least.

[ShinkenW]

It doesn't solely come down to how many of the original actors Toei could or wanted to bring back, it's really a combination of that AND what the writers want to write about, and the characters that THEY want to bring back for their storylines...which often also depends on how many of the original actors Toei could/wanted to bring back. So it really comes down to both the company and the writers themselves.

Personally, I would've even preferred if the arcs were written in alternate realities but with some of the original casts and set in the same world as the original seasons...as oppose to alternate worlds with completely new characters. And I don't care how other people feel about that, because after all, we all have different preferences.
But I just want to say, wanting to see original characters and old faces back don't necessarily mean fans are "not thinking about what's important"...there's no gimmick, many fans want to see old faces back because we love them and it's difficult for many to warm up to new characters that replace the originals, that's true. But many still care about the storylines too. And bringing back old faces don't necessarily impact on the quality of the storylines either.

In the case of storylines, I thought the tribute arcs were good...among the tribute arcs for seasons I have watched, I especially liked Kuuga, Kiva, Kabuto & Den-O's arcs...however, what was the let-down for me was the new characters, I just could not warm up to them (except for Yusuke, and Den-O because it had the original characters), and that unfortunately did affect my viewing experience, even though I liked the arcs story wise. I didn't like Blade's setting and story, and neither its new characters. Agito's setting & backdrop in the arc was pretty much the same as in the original series, so I had no complaints about that, but the new characters were so blah to me I didn't care for them.

Sometimes just having good plots is not enough, if the characters fail to impress the viewers, then surely that would affect one's viewing experience and that in turn impacts on their judgment. No doubt I have troubles accepting the new characters in the tribute arcs for the seasons I've watched, but not the storylines...it's just a pity that virtually none of the new characters in the tribute arcs for the seasons I've watched appealed to me (there's only a few exceptions). I really wished that I would be able to warm up to much of those new characters, I'm sure I would've enjoyed more of the arcs and Decade overall if I do, but sadly I don't.

[Captain Platypus]

What is with the Den-O hate? Seriously, it was a good show

[ShinkenW]

^ it seems some people simply hated the cheesy comedy of it and prefers a season with a little more seriousness and not so light-hearted...

I agree with you that Den-O was a good season...but it's one that is ideal purely if you just want to chill out & have a good laugh, it's really not a season to be taken seriously, like Carranger.

[Captain Platypus]

Den-o had some real deep drama. Why do people forget how screwed up some of those characters were?