Thor from Pirate Software has a great video breaking down how Steam works and the lawsuit that claims they are ripping off consumers. It’s very educational.

Of course, there is no requirement to use Steam. Game makes can publish their game themselves without a platform at all, which very few do. If you say they actually need a platform, there is the value they are getting for that 30%. If they weren’t getting anything of value, then they could do it themselves and benefit instead, which most do not.