Huh? Nier Automata has sold over 4 million copies and the upcoming Babylon's Fall and Granblue Fantasy look pretty amazing as well.
Ironically enough I was just talking about in another discussion on the site how great Nier Automata's multi-platform sales were.
While I agree with you that Platinum had a lot of success in-between Nintendo releases, in fact their largest success (and you can even look at stuff like Metal Gear Rising Reveangance or Bayonetta 1 which were all successful, Bayonetta 2 not getting a publisher mostly because Sega was near bankruptcy), Platinum has been treated inconsistently by most publishers.
For context - Platinum Games actually got kicked off Granblue Fantasy, and Babylon's Fall was announced E3 2018 but hasn't been shown at all since, and despite an Automata sequel being hinted at many times it doesn't seem like Platinum is actually going to be involved with it this time around (considering they only have 200 staff but are working on Astral Chain, Bayonetta 3, Babylon's Fall, Granblue Fantasy, and at the time of the first Nier Automata sequel tease - Scalebound was pretty recently cancelled).
It just seems like they're doing a lot without getting much credit or success. Wouldn't be surprised if Babylon's Fall was outright cancelled. They seem like the studio that sort of needs commitment from a publisher.