Disclaimer: I have never watched a single Ninja stream. I'm not a bias fanboy of his or anyone on the platform.
But I can add two insights:
Twitch also removed Ninja's subscribe button after he made the decision to change platforms. This seems like a really immature thing to do and they are choosing to burn bridges rather than being professional. Removing the subscribe button effectively stops him from gaining tens of thousands of followers in the time between switching platforms and the only reason they did it is because they are angry he is leaving.
Other streamers and youtube personalities that work with twitch have stated on different occasions based on their own interactions (unrelated to Ninja) that Twitch doesn't seem like a professionally run company and more of a wild west or a frat house.
Im not sure if this one is just a rumor but I've heard Twitch holds company events where employees mingle with certain personalities on their platform which may explain the preferential treatment some streamers receive compared to others. Its not that scandalous so I'm inclined to believe it. I understand a company having get togethers and inviting top talent but the fact there is known preferential treatment of certain streamers paints this in a bad light.