Ah I see, you're correct, I did misunderstand you. I think your point is true, but still lacks finesse in describing the relationship between developers and digital store fronts. I also think you're disregarding the benefit that the additional 18% cut the developer gets to keep as well as creating partnership options rather than being stuck with a defacto monopoly.

I also don't think it's fair to compare GOG or Humble Bundle with Epic or Steam, their purposes and market share is so much smaller than Steam. Epic isn't trying to compete with GOG or Humble.

Also, you're correct that the developer is making money either way, but they are making a larger percentage on sales through Epic. You're probably right that the developers aren't taking that into account, but they are materially benefited by its success. If they fail to account for that benefit and Epic fails then it will mean they make less money overall.

I think instead of your McDonalds example a better one would be contractors for a large business. Maybe your business frequently uses an electrical contractor and due to special circumstances the field is exceptionally limited (specialty license or security clearance). There is one contractor available and they have a monopoly and can charge whatever they want. So far this company has been really fair and not abused their power, but a new contractor becomes available. The new contractor has an inferior service line and is a bit slower, but they're also cheaper. You could just ignore the new contractor and what happens happens, but in the real world it's fairly common for businesses to diversify service contracts to maintain a pool of available contractors.