If they charged less.fpr the platform, they'd still be raking in more than they can spend while also not taking an extra 20% out of game development budgets versus the competition.
As a consumer I'm more concerned about Epic's anti-consumer practices than what they are paying devs.
Talking about how much they could charge devs does not change my experience as a consumer. It does not provide a compelling argument for me to use a service that does noticeably make things worse for the consumer.
You think Valve taking an extortionate amount of the budget doesn't affect you as a consumer?
Games have budgets. With Valve taking as much money as the actual development budget for many games, the end product is significantly impacted. Games are regularly released late while missing features and so buggy as to not work. The extra 18% of the gross taken up by Valve versus EGS could be used to put more resources into the actual game.
Walmart and GameStop provide a physical place, that's it. The Developer sends them the physical product.
Steam provides unlimited downloads, user forums, automatic updates, remote play, user reviews, Steam workshop etc....
None of these other stores provide these things.
Maybe Epic should charge more than 12% and invest that money in improving their client, or at least do that instead of wasting it on exclusivity deals. Then maybe I as a consumer will give a shit about Epic.