But they are competing on the quality of the platform. What do they have a monopoly on? Being the only place to watch Star Wars or whatever is not a monopoly. They compete on both the quality of the content and the quality of the streaming experience.

If Disney doesn't make much content that I want to watch (and they don't), then I don't have to pay them a dime for anything. If HBO only makes one thing that I want to watch, then I can subscribe for a month and then pay them nothing after that. That's a significant improvement over the previous way of doing things.

Why would it be good for a single company to control distribution of all content?