They could try to do both things (delivering new packages and taking back containers) at the same time.

https://en.wikipedia.org/wiki/Milkman

http://pocketcultures.com/2012/01/25/argentinean-customs-hav...

My guess is that the returning of the supplies could result in a lower carbon footprint. The whole delivery system is optimized for getting products from supplier to receiver, so there's a decent amount of unused capacity for getting items back into the delivery system. The "last mile" delivery trucks progress from full to near empty throughout the day and likely already pass or get super close to homes that could be returning packaging thus keeping the vehicle near capacity throughout the day. Once back into the delivery network the returning packaging should fill existing extra capacity especially as it get's closer to the supplier where they're already shipping out a much higher volume than they are receiving. Just a guess, but that's how I've rationalized it ;)

When I found out that Tile offers mail-in recycling for their trackers, I wondered the same thing. Perhaps this service is offered to assuage the guilty conscience of people who would like to buy a tracker but feel bad about buying something they'll throw away. But if it's something that can be recycled by the company (again, at what cost?), then it goes from being disposable to "reusable".