It happens because Twitch is a platform for anti-American and anti-Western propaganda.
Hasan Piker has made threats under no uncertain terms, wishing harm against his political opponents. There are massive compilations of clips, videos, and evidence for his activities, and yet Hasan doesn't get banned.
What Hasan says is not subtle... nor are they jokes. He tells people that America deserves 9/11, reposts a politician's comments with a schematic of the makeshift gun that killed former Prime Minister Shinzo Abe, telling his followers to "kill" capitalists, plays terrorist propoganda and praising it, glamorizing actual terrorists on stream, etc...
The staff and leadership at Twitch have collaborated with Hasan multiple times, and based on their moderation actions, it's VERY clear that Twitch's staff has a very left-progressive political viewpoint.
Hasan's viewer base and his fans are rabid attack dogs who attack anyone that are critical of him. Harassment, mass reports, doxxing, false flagging... even credible and actionable death threats. Some of his viewers and fans have committed serious crimes.
He is dangerous because he commands a large audience that is mentally unwell, violent, and extremist. At the minimum, Twitch should have a proportional response towards Hasan's behavior, but nope... he is their golden boy, and they will protect him no matter what.