Meanwhile Twitch has locked in many of the creators with 24 Hrs platform exclusivity. High viewership count twitch streamers are not going to risk their twitch partnership status because Facebook is offering some subsidy.
There are several "High viewership count twitch streamers" who moved to Facebook because they got a much better offer. DisguisedToast, KingSlayer, Corinna Kopf etc.
Also there is still a difference between someone like Asmongold who pulls 100k viewers and has fuck you amount of money and others with 5-10k viewers. 5-10k makes you a 1% on Twitch but you are still on another league from Asmon, Shroud etc.
Last but not least seasonal fluctuation is real for a lot of streamers see the current WoW worlds first race where the racing guild memebers are having 30-50k viewers but that's gone next week when the race is over.