The economics of a game engine engine business are grossly inferior to an app store. Steam charges 30% of gross (25% at high volume), Unity charges by seats and not fees after (huge backlash when they tried to go the other way and indies bailed to GODOT.) Unreal Engine 3.5-5% and maybe some seat fees now.
If you were a developer you are looking the other way, getting those app store fees down.
The App Stores - Steam, iOS, Google Play, are making higher margins per game than most game devs, and that's based on hard numbers not a guess. There is no meaningful way for game developers - artists, programmers, and everyone else involved - to make more money other than getting rid of the app store fees.
There is a whole explanation about network effects here, and endless debate about what the fees should be. There is a cost to sell a game and it is not small. Several percent just go to credit card processing, refunds, and fraud. More has to go for the infrastructure to deliver games and updates. Then there has to be some margin. Then there maybe should be a premium that goes to the "app store" so that developers don't have to worry about distributing their app to thousands of locations. There is another premium that really is delivering demand for the game in the first place. Many sales would never happen on Steam if the users were not shown the game as featured or recommended. Most developers have no problem paying 30% for a sale that would otherwise never have happened.
However, if I went back in a time machine to 1999 when you drove to a retail store to pick a game box off of a shelf, and you told me some arbitrary application would get to take 30% of all game sales decades in the future, I would have said that's fucking crazy. More developers should be able to seamlessly sell their games direct to their players, and I'm not entirely sure why they don't. Selling a digital item online is definitely simpler than developing a successful game.
Edit: And if you look at Unity's financials they are in real trouble and probably will only survive if another larger, profitable, company acquires them. Not a great feeling for game developers who might suddenly be paying Facebook/Meta or someone worse their license fees.