The driver signed the contract to work for a business. Maybe the contract specifies the delivery fee going to him, maybe it doesn't. If it does not, he gets what he is due in the contract. If he doesn't like it, he can quit and go work for a business, which pays him more for the use of a car. If a company pays less than the services are worth, it would have no employees.
I don't really see the issue. If you'd like to help the delivery drivers, tip them.