How so? And under all circumstances, or only for some cases?
We already have mail delivery systems, which scale pretty well AND can be augmented by bots and other technological advances. I have a hard time seeing how your claim holds besides some corner cases like "need fresh tomatoes for cooking in this evening".
I could see it happening as an intermediate step, before everywhere has automated delivery.
Similar to how there are smaller stores that don't accept credit cards yet, most shops probably won't support any sort of delivery either. This is already being addressed by services like doordash/grubhub/postmates/etc, but it'd be cool to have your own personal doordasher that you (presumably) could pay normal store prices with.
I do think the more likely scenario though would be somebody like doordash firing their human delivery drivers and just having robots/drones do it instead though.
To me this still sounds a lot like "everyone buys private helicopters before affordable flying taxis are a thing".
An autonomous robot suitable for generic (or even a few select) tasks is rather complicated and/or requires non-trivial infrastructure at the site of service (e.g. grocery store).
For example a carrier bot following the delivery person is much simpler in comparison and can increase the efficiency of the mail delivery system without putting new infrastructure in place everywhere. With standardized mail slots some deliveries could even be automated (still less complex than a robot at every shop the fills up your robot or your robot having picker capabilities; plus your robot might need your car to get around).
We already have mail delivery systems, which scale pretty well AND can be augmented by bots and other technological advances. I have a hard time seeing how your claim holds besides some corner cases like "need fresh tomatoes for cooking in this evening".