That's the stupidest thing I've ever heard about Kiva and you're the only one I know of that has said it. Young boys weren't even interested in the books and the movie wasn't even released in Japan until after Kiva ended which is when the series peaked in popularity. You can't cash in on something unless it was popular with the target demographic.
As for having Kamen Rider become an anime? No, that would be incredibly dull. I wouldn't mind seeing a Kamen Rider special as an anime but not a full length series.