One word: variety.
My local sushi place isn't going to have enough delivery orders to justify having delivery drivers on staff.
Heck, I remember years ago (Was it the late 90s?) when McDonald's tried to do delivery.
But yes, their business practices suck, and that's our fault as a society for yet again allowing capitalism to run amok.
The problem of course is that a restaurant that refuses to work with deliveries then ends up getting significantly fewer orders than ones that do. It creates a bit of a racket. Restaurants feel forced to cooperate, or lose significant business.
As a customer, I get around a lot of the extra costs because my credit card gives me the Dash Pass for free as a little bonus, and Costco sells $100 DD gift cards for $80, so I'm effectively getting every deliver at 20% off.
But delivery sushi? Delivery pasta? Delivery tapas? Delivery burritos? Delivery Korean fried chicken? Delivery acai bowls? Delivery kebab?
DoorDash etc. gives us a variety of options that we mostly didn't really have before.
I do agree with you on the bullshit of turning employment into disposable contractors. But maybe we should change our laws to make that not possible, instead of condemning the idea that it's actually neat to be able to get nearly any kind of food from nearly any restaurant delivered to your door. We didn't used to have that.
Now, everyone is offloading their deliveries to DoorDash. Wendy's first-party delivery is just a wrapper for DoorDash. Pizza Hut used DoorDash if they don't have enough drivers available. Even PetSmart or Petco uses DoorDash for delivery now.
Not saying it's right or good, but you could order from Pizza Hut and still get a gig worker if their driver called out stick today.