How exactly is getting a better rate for game distribution "selling out?" Supergiant benefitted themselves and their developers by getting more money for the ga

How exactly is getting a better rate for game distribution "selling out?" Supergiant benefitted themselves and their developers by getting more money for the game. I don't understand the vocal support for Steam over Epic Games. Steam literally charges you more and there are no competitors as big as Steam. I'd rather have a de facto duopoly vs a monopoly. And yes, I'm aware of GMG, Origin, Blizzard, etc.