To add to this, many of the most popular airports with business travellers (LHR, JFK, HKG) have restricted capacity. They'd have to use the same number of slots

To add to this, many of the most popular airports with business travellers (LHR, JFK, HKG) have restricted capacity. They'd have to use the same number of slots for a small supersonic plane as for a widebody flying that route otherwise. That can significantly increase cost per seat.