The problem is not a lack of two-bit cartoon mice in the public domain. It's that this one particular two-bit cartoon mouse is being protected by a very wealthy corporation that has lobbied for extending copyrights to the point that very little will enter into the public domain anymore by aging out.
Want to do something with a story or novel or song from 80 years ago that no living person was involved in producing? Sorry, you have to license it. We don't know who the license holder is, but we won't fund you because we're afraid someone might turn up once we release your remixed story/movie/song and then there'd be a lawsuit and that's just a mess.
Our cultural heritage (for better or worse, not sure I like seeing Disney and company like that) are locked away so that it's very difficult to do anything with it, compared to properties from anytime before Mickey came into existence.
Eh, I don't care a whit about Mickey Mouse. I do care about all of the post-1923 literature that is really hard to find because it is locked up under copyright, but not profitable enough to get reprinted by the rightsholders[1].
I'm also concerned about all of the film, television, audio, and software that is in similar copyright limbo. There's a lot of stuff out there that there simply is no legitimate way to get access to.
