It is my understanding that the management company of Shroud Grzesiek, Loaded, is the same one that "Ninja" had. So it seems like these moves are more a thing of a partnership between Microsoft and said management company, than just a movement that the streamers came up by themselves. I guess it makes sense, they wouldn't risk their livelihood otherwise.
Regarding the Twitch situation, I am not very well informed on how one-sided is their treatment. I am also not sure how many more options Mixer has to interact with your public. Last I read, they had a better resolution available than the top Youtube Live and Twitch can offer. Something I can say for Mixer is that their Low Latency Mode works well and I have been told the viewers in chat are in general nicer than the ones on the other platforms, though I am not sure if that still holds.