What about Amazon? Or any other dominant player in any market?

Steam does not come pre-installed on nearly every device unlike Apple's and Googles offering. Future Steam Deck not withstanding, but that will be miniscule player.

They don't prevent any other store from operating. So I don't see how they are comparable to anything Google or Apple does. Windows Store might qualify if they forced themselves on Windows in same way. But certainly Steam is entirely different.