> I think last mile is an interesting problem but OP seems to be intending to build full transit logistics infrastructure built on casual labor, which seems unlikely to pan out.

I think we are unloading a lot of expectations on the OP. Maybe this was just an interesting thought experiment to them - "how would I solve the cold start?"

> Maybe FedEx/whoever is closing the gap when they can’t get everything onto real delivery trucks and this is more cost effective than buying more trucks and hiring more drivers?

Ah fascinating! This could explain why I see this behavior across multiple retailers. My initial hypothesis of "the retailer wants to see me happy" is now supplemented by "UPS/FedEx wants to see their retailer customer (not I) happy".

Free markets are fascinating and Thank You for offering this new perspective.

> Maybe this was just an interesting thought experiment to them

Possible, though OP says they are “About to launch the MVP”.

> ”UPS/FedEx wants to see their retailer customer (not I) happy"

Just to be clear, that was my guess. I’ve done no research on this specific thing so maybe some other factor is in play with these packages delivered from private vehicles.