Why is the delivery service concerned about the food quality at all? Post office is not concerned about quality of products it ships and I don't see anyone expecting it to be.
The Postal service is a utility competing on efficiency and price. That's not what "tech unicorns" get billion dollar valuations to compete on. Tech is about building a "platform" to siphon off money for all eternity while doing little of the ongoing labor of delivering or producing the value. To build that platform you need a moat, because otherwise somebody will come in a compete on price, so you build brand loyalty by gate-keeping the quality of stuff on your platform. That way any competing platform will initially be primarily populated by all the stores too "bad" to be marketed with the incumbent.
It's quite simply not financially lucrative enough to run a utility for venture capitalists. In a more sane, less inflated economic climate, this might change.
Because they aren't just "delivery services" and don't want to be, as a delivery service (or any other sustainable, boring "utility business") has poor potential for monopolising a market and the "growth & engagement" VC tech-bros want.
It's quite simply not financially lucrative enough to run a utility for venture capitalists. In a more sane, less inflated economic climate, this might change.