I've never understood why companies choose to delete videos rather than just monetize them. I've uploaded videos with copyrighted music, rather than get deleted the owners chose to have ads shown in my video(my channel is unmonetized) and I'm assuming they make money from it.
There are certainly some cases where this makes sense. In the extreme case, suppose someone uploads a full copy of a new movie. It seems unlikely the studio would make up for the revenue from lost ticket sales with just ads. They might be violating contracts with their distributors as well.
