The purpose of superchargers is to deliver as much power as possible in the shortest amount of time to maximize availability.
While your perception is that a installation will not be maxed out during dinner the possibility exists. I personally have gone inside for a snack and 20 minutes later the supercharger, empty when I arrived, now only has two available. This was in the middle of nowhere Pennsylvania, late at night on a Sunday. If I left the restaurant for a few minutes to move my car to make room for others then so can everyone else. With thousands of Model-3s being added to the fleet every week we need the correct mentality in place. The already congested infrastructure is about to be overwhelmed.