Because problems inevitably occur and with full time staff it's more likely the delivery person has seen the problem 1000 times and knows exactly how to handle it optimally. In addition to knowing the ins and outs of your office or apartment, perhaps even recognizing you by name.

> I'd expect them to make better deliveries and more accurately.

I wouldn't. I'd expect the additional supply would get you faster, cheaper delivery at the expense of accuracy and a slight increase in other problems. I'm not against that trade off but there's no need to pretend it doesn't exist.

> Uber/Lyft have shown this model works fine.

Uber/Lyft and particularly Lyft where you're less likely to get an experienced professional, have shown that the model is not without it's tradeoffs.