Everything is a tradeoff. Your grocer probably feels that customers appreciate lower prices in exchange for that setup.
There may also be an upscale grocer down the street that tends to provide ample staffing at checkout lanes.
The problem due to the monopoly held by the postal service, its system is not subject to competition. Competition might result in competitors trying new approaches with similar staffing (improving processes, etc.) or in different staffing levels and even better service.
It's hard to know what all the clever people actually doing the work would have come up with, since their jobs will never exist when there is only one entrenched monopoly.
There may also be an upscale grocer down the street that tends to provide ample staffing at checkout lanes.
The problem due to the monopoly held by the postal service, its system is not subject to competition. Competition might result in competitors trying new approaches with similar staffing (improving processes, etc.) or in different staffing levels and even better service.
It's hard to know what all the clever people actually doing the work would have come up with, since their jobs will never exist when there is only one entrenched monopoly.