Follow the actual law
https://www.law.cornell.edu/uscode/text/17/512 Twitch needs to look at the actual letter of the law and unless the person doing the strike does everything as required in paragraph section C. Paragraph 3, Subsection A, no strike is valid or legal as ruled by US Ninth Circuit Court in Lenz v. Universal Music Corp resolved on September 14, 2015
RainmanUSMC shared this idea
Twitch would rather pass along the responsibility to the streamer than to get into a (costly) legal battle with the music industry. That's why they're bending over backwards for the industry. It's the cheaper solution for them.