Epic’s 12% doesn’t do much because they’re constantly burning money trying to find more revenue. It’s obvious they’re not doing anything efficiently. They also have far fewer sales than Steam which further hurts their bottom line.
The standard internet payment processors take 3% as their cut.
With modern cloud systems we can quickly distribute files globally for tiny amounts of money.
The truth is that Valve makes a ton of money off of this fee. It’s great that they contribute to open source projects but plenty of companies make similar contributions with a fraction of the resources.