I cannot do that if there is no existing customer base like in those examples.

This isn’t about it being impossible to circumvent steam as a dev. This is about Steam being so powerful, that they can do whatever they like. That’s why they’re a quasi monopoly, not an outright monopoly.

Not putting your game on Steam is only viable for very few developers these days. Besides, WoW, LoL and Minecraft released and gained traction in a time, when Steam was not nearly as bis as they are today.
Back then a most games still shipped on DVD with either disc based copy protection or a number of other launchers (Ubisoft Game Launcher, EA Origin, Games for Windows Live, Rockstar Games Launcher), which do mostly still exist in one form or another but drifted into irrelevance as Steam grew to the near insurmountable power house they are today.

Or do you think EA, Ubisoft and Rockstar would put their games on Steam, paying a 20-30% cut of each game sold to the store, if they wouldn’t lose more money telling people to get their games on their own, existing distribution systems? (something AA and indie devs do not have)

And I’m not saying Steam didn’t earn its crown. They are feature complete, mostly pro consumer and have a less shit interface than its competitors.
But if they decided tomorrow, that devs had to pay 10% more per game sold, most devs would have to budge or sell significantly less games.

And they might, when the day comes that Gaben isn’t in charge anymore. And we’ll all have to take it because their competition is either too small (GOG) or too stupid (Epic) to properly compete. And I don’t like that. I’d much prefer Epic didn’t suck.