IIRC (from what I've heard from friends/acquaintances, so I can't guarantee this) the way that (at least some) have enforced "X only, no UberEats/etc." is by putting it in their contract and saying "we control 75% of the ordering traffic in your market. If you want on our app, it has to be exclusive".
As a consumer, my cost for using ten different delivery providers is nil. If there's a constant trickle of new entrants always giving away the store to attract me to sign up, I'd be stupid not to use them all.
As a restaurant or driver, they'd have to offer some very expensive incentives to make me say "DoorDash only, no UberEats/etc."
I feel like there was a large bet made on autonomous vehicles being ready before the music stops. Once you no longer have to hire human drivers, the "big ball of capital" model works better-- buy a million robovans and you can provide a service level or geographic scale no new entrant can match without a similar up-front spend..