Example: I order a pizza through Deliveroo. The driver doesn't care about either the restaurant or me, so he chucks the pizza vertically in his box, ruining it. I get a shitty pizza, I won't order anymore from the restaurant.
Compare this with me calling up the restaurant and having one of their employees delivering the pizza: the restaurant has all the incentives for me to enjoy the pizza, since they suffer if they lose me as a client.
And no, it doesn't help using something else as deliveroos: the deliverers are all the same (they use multiple apps) and they don't give a shit about the quality of the service (and rightly so, since they are paid peanuts)