Probably because the voting was rigged. Showa had a small but significant lead in the online poll and the theater poll numbers were not enough to make up for it.

Poor Showa....so unappreciated...

Oh god not this shit again. We just got done accepting the fact that Morphin' Madness wasn't gonna turn out the way we wanted to.

Booo!

Hissssssss!

Ah well. Let's hope we get an alternate ending at least for the home release.

Heisei is the best rider era. They have my favorite rider Kamen Rider Double

When I first heard about this it was a huge SHOCKER to me. I was routing for the Showa Riders but voted for Heisei because my favorites are Heisei but the Showa Era is growing on me.

That is quite surprising. I would have figured Showa would win.

Yeah for Heisei! Although I'd like to see Showa Riders beating a few Heisei Riders in the movie to show they aren't pushovers.

Don't worry. I don't think they'll make the Showa Riders look like bitches. They just won't succeed in the end, is all.
Unless Decade is involved in any significant manner.
Because they're still trying to sell Decade to the audience, so they'll do anything to make him look cool.