The thing is, there is a business there but it only works with economies of scale. If they're constantly focused on eating each other it won't work because you have multiple "networks" each with a finite, unevenly-distributed share of supply (restaurants), delivery drivers and demand (customers) that can't share load between each other (so you end up with situations where one company's drivers doing nothing while another one doesn't have enough capacity - both end up losing money).

A business providing ultra-fast courier service providing order matching & routing that otherwise stays neutral and charges a delivery fee (as opposed to skimming off the entire bill) would work.