If I buy a game on steam, I should be allowed to sell it. Just like I’d be allowed to sell a physical game.
If I buy a game, no DRM claim should be able to claw back that game from me.
It's the exact same product - the perceived difference is a mirage. Digital media is the only product that works this way, and it's stupid.
Platforms and stores would have to, I don't know, actually compete then. Who offers the better experience? The better price? The better device? Not "You bought your shit here, so you're stuck. Sorry"
Platform holders should take a cut of anything sold on their platform, but it's because a user chose to buy it from them because they offer a better service, not because it's the only way they can use it.
My reservations about DRM aside, you can still achieve this without dropping DRM. It would have copy protection still.
The seller isn't selling it to you. They're "licensing" it to you. You could "sell" the license. That's just paperwork (that they in no way are obligated to make easy or support facilitating your ability to do, mind.)
This is the new world that the business schools have wrought for you. Don't you like it?
"If I buy a car, I should be able to drive thru train tunnels."