Yes, it is different for shops. For hospitals you are attending an appointment, visiting a patient, making or collecting a delivery - all of which require interaction and where a token can be passed to you. Someone with no business there would immediately fail that interaction test and then they have the problem of getting out of the car park with no token, unless they pay.
Yes someone can overstay, but how many times have you genuinely visited a hospital and decided to leave your car there while you go to work? It is not a likely, regular occurrence and would have little impact on day to day parking levels.
SteveW