Doordash etc has its value. It is not for me but I have seen and use it a few times for what I need.
1) Company meals so they don't have to deal with corp card abuse and labor to check it (time is money remember),
2) Ordering food from far away that is cheaper than where you are at locally like when I am in a tourist trap hotel and the food is cheaper to doordash from 10 miles away and better. Obviously if it is just downstair from my apartment building it makes no sense to doordash.
3) If I need to order something from opposite direction far away, or if I need to order say for 20 people, doordash or waiter.com would work well but not me driving all over with an empty trunk, etc.
About pay later: it is just like credit card loans but at a more focused type of meal. Some lenders would take that risk and package it as investment to sell to others. It might be cheaper than credit card debt, because it is probably lower risk (you can have a smaller credit limit), and it is probably better than credit card debt for customers and lenders alike.
Something to think about on cost and expense: when I am working overtime and company pays for my doordash, the woman deliver my meal has a kid in the backseat in a carseat. She is making a cut, she is making money while watching her kid (so she can't do uber, only food delivery), the company from far away making my meal is making money, my employer is making money because I'm working, I am making money because I don't have to take time off work to drive and get my meal or cook and then work overtime later. That's how economy should work: people provide value to the economy on what they can and let others doing it either better or cheaper.