Why doesn't Riot unban XJ9?

Because he was a toxic bully who actually could have and should have been prosecuted by the police for some f the stunts he pulled in league.

He was probably the most toxic player in history. It went beyond the games. He stole accounts. His gf played Lee Sin, a champ he hates, so he decided to spam facebook with nude photos of her. Then he hijacked her account and spam lossed it to oblivion

Here is a 14 part series of his talk with destiny justifying why he was right to post the pics: https://www.youtube.com/watch?v=bc7ZMDRbF2s

It didn't stop there, he was eventually banned and made a huge long post here about he was a victim and didn't do anything wrong. Riot employee showed up and basically said he would never be unbanned and that he had sent numerous death-threats including to Riot and women. He was essentially stalking his ex and harassing her: