> It's cheaper for me to drive to the restaurant and pick up the order
Of course it is... were you expecting delivery companies to perform magic while humans are required to bring you your food?
If a burrito costs $15, it may cost $30 to have it delivered from 20 minutes away; the alternative is 40 minutes of your time and $15. The thesis of delivery companies is that you value 40 minutes of your time more than $15.