My guess is sort of a combo. He's enough of a part of the old establishment that needs to go, so there could have been some pressure from above for him to step down. Plus his negative training methods have been called out in public recently, so that doesn't make him look too good. And on top of that, Sam Peszek has mentioned that her mom (who is a USAG employee) and family have gotten death/rape threats recently so it wouldn't surprise me if Valeri and his family have as well, since he's way more involved and public than Luan Peszek is. He might just be done with all of it.