You also recognize that 30% of each game sale applies to each game sale, right?
Do you really think 30% of developing a game is hosting not just the original game, but also the updates and the save files? CDNs only make it cheaper.
Steam is able to charge 30% because they effectively have a walled garden on PC games. Very few publishers are well known enough to successfully sell their game outside of Steam.
It’s not as egregious as the Apple or Google stores, but they’re basically all in this together. It’s like the old mob families where they split territory.