Not only movie theaters, but also movie rental and selling of VHS tapes/DVDs etc.

One could go to the favorite department store and get movies from all studios right next to each other, sorted by genre or title or similar.

Music publishing vs radio stations is a fascinating example - compulsory licensing, meaning radio stations are free to broadcast any music at all; even rules preventing radio stations and DJs from accepting payola from publishers to promote their records.

Like vertical integration isn't always bad 100% of the time, but this particular case of marrying distribution and production seems to serve minimal beneficial purpose and inevitably the main outcome is high levels of rents-collection and squeezing the people doing the actual creative work. There's pretty much nothing but up-side to forcing the two roles to remain separate.

It's probably got something to do with copyright. Like the way it interacts with markets makes this sort of arrangement net-harmful pretty much any time you see it.