> If there is uncertainty about whether the food is coming or not, there is no reason to use the service.

And what I'm saying is that there's already uncertainty. The current interface of DSPs showing that it'll arrive within 30 minutes or whatever, is a leaky abstraction of how the underlying system (ie. restaurants and delivery drivers) work. Just as how DSPs likely have some sort of system to estimate delivery times based on current supply and demand, they can build a system that also factors in price, and give consumers various price options and their associated estimates.