In Sweden there's a popular food delivery service that simply ties together restaurants and taxi drivers. This eliminates the need for round trips, since the taxi driver can just find some other fare for the return.

This works fine in Sweden which has a deregulated taxi market (=no shortage of available taxi drivers), but it wouldn't work in SF which has such an artificially constrained supply.

Any moderately busy pizzeria will queue up a few delivery orders that end up being ready at around the same time, and will have one driver deliver them all within a single trip.

The trip may take marginally longer than if just one order were being delivered, but it ends up fulfilling five or six orders with one trip. The cost per order ends up being decreased to a reasonable level.

You are right of course but there is also the possibility of loss leaders. And many times in business things don't make sense on the surface but play out differently. Perhaps they will have add on items that will generate more profit. Perhaps the amount of people who only order bread alone will be small.

If they get funding they have the staying power to test the market and potentially find profitability. That's the big big advantage of using "OPM" when starting a business. Not guaranteed but not a non starter either.

One big benefit of starting at a low price below costs (if you can) is that it keeps others out who think "we can't make money doing this".