Indeed, I don't like how the delivery companies double-dip by charging both the restaurant AND the customer for a delivery. A modest fee of like 5% to the restaurant would maybe be fine (Especially considering the restaurant is already likely paying 3% for credit card processing), but based on the price differences between DD and the restaurant's own menu, it likely 15-20%.
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.