It seems you’re conflating trademark and copyright. Personally, I’m fine with trademarks continuing in perpetuity as long as the owner maintains the registration. Disney gets to keep their brand name and trademarked characters. It’s copyright on Disney’s films and music that’s the problem. Maybe I can’t make my own Mickey film, but I could certainly remix Steamboat Willie cartoons if they entered the public domain. Or do similar with their music. But it’s really not even about that. If Disney gobbles up all the copyrightable content, maintains copyright forever, then creating something new (but too similar) can put an individual artist in trouble with copyright law. That’s unacceptable.