The issue is treating all third party stores as side loading, when no other category of device does this. It violates EU anti trust laws, and possibly US antitrust laws as this lawsuit explores. We trust people to have figured this out for PCs and macs, mobile is quite literally no different at this point.

Valve provides unlimited bandwidth for the rest of eternity for your game in exchange for a refundable $100 deposit and 30% of sales, with exceedingly few rules regarding what you put on the store, all without ads, optional additional FREE revenue streams in trading cards and marketplace items, and free unlimited bandwidth for mods via workshop integration; not to mention free Multiplayer matchmaking and unlimited free steam keys you can give out or even sell on secondary markets with very few restrictions. Neither itch nor gamejolt can financially offer half of those features, and no other publishing platforms comes close to offering all of these features, much less all of these features at such a ridiculously low cut as valve takes.