Why is every good TV show Cancelled
I don't think it's by plan. I think seasons keep roughly ending up in the same places by the end of seasons accidentally. They want more Riders & evil Riders are an easy way to breed conflict. Besides, several of the first long term evil Riders-- Riderman, Shadowmoon, Ouja, Leangle-- were well received. Eventually ending up in a war is probably the easiest way to reach a peak in the conflict. At least, they pulled back on that in Zero-One & I doubt they can really do that this year, either, whether they wanted to, or not. But, to be fair, I think they had some inspiration for Zero-One's ending from current events. That doesn't happen with every story you write.