I'm visiting Southeast Asia right now and Grab is a popular service.
It seems to me you can order anything (reasonable) from Grab, but it seems 95%+ of the orders are for food
I think the other thing that makes delivery here simple (and I'm guessing, profitable) is the proliferation of scooters. They're everywhere and everyone has one. I suspect decent gas mileage and simple to park convenience makes them the obvious vehicle for instant delivery.