Because of the complete ****** she's turned to in her actual life. Disney channel didn't want to baby her anymore and struggle keeping the junk she's getting into off tv. Disney channel was going to crash and burn if they had such a *** on their channel. Disney channel is supposed o be a super sweet super perfect super nice kiddie channel and miley cyrus was not helping them out with that image. I'm pretty sure she didn't quit, she got fired.