Not everyone shares your views. Most people probably don't, and Twitch wants to keep the majority happy, not just you. But more importantly, advertising. Once

Not everyone shares your views. Most people probably don't, and Twitch wants to keep the majority happy, not just you. But more importantly, advertising. Once you're known as a website with lots of pornography, expect your cost per ad to drop to about 10%. And with potentially unmoderated adult content you risk having all major payment providers refusing to do business with you. See what happened to Pornhub about non-verified user uploaded content a year or so ago. Requiring things like uploading ID in order to stream will harm the non-adult segments of Twitch. So unless they want to go full-on porn site, mixing adult and non-adult just harms the rest of the business.