You forgot what drives every good for consumer thing a company does: competition.
If every games company is allowing users to resell their items, and Epic is not, they just look evil. We're not there yet but when we are you don't want to get the reputation of being the evil company that seeks profits above all else.
Social media companies "look evil" when they don't allow users to freely use third-party apps and clients, but they still don't, because that doesn't make them money.
And competition doesn't/won't solve either problem, because third-party apps aren't why most people choose social media platforms, and reselling hats isn't why most people choose a game.
In other words, the proposed feature is something developers want, not users.
That still leaves you with the chicken-and-egg problem of how you get to the point where "every games company is allowing users to resell their items", when it's not beneficial to any of them to start with.
