He's been a locker room cancer his entire career, including college at UCLA. He was a good enough pitcher for teams to deal with some of that, but that was Cy Young level pitching the year he was using sticky substances. He doesn't listen to coaches, he doesn't listen to catchers, he's an ******* to teammates. Once his pitching started to fall off, he started using sticky substances and won the Cy Young. That pitcher doesn't exist anymore, and teams don't want to deal with his BS anymore.
The rape allegation gave teams an excuse to get rid of him and ignore him for good. He was already pretty universally disliked before that.