I think it's cause Kamen Rider is still a niche series compared to more popular and profitable franchises. Plus those games you mentioned are getting localized, which turns in more profit. And IIRC, the PS4 isn't doing so well in Japan, so it makes sense that they would want to make BW3 for the PS3. It's easy to do (Just reuse the assets) and can probably churn more of a profit than doing a cross platform release to a less popular console. But who knows, they surprised everybody with the first Battride War game being on the PS3. I remember people flipping out when that was first announced.