<<I suspect it is to do with Insurance. The German tourists who were killed in the Air France crash were all quite wealthy>>
Doubt this - with all respect, the film stars and business types flying to and from JFK each day I suspect are better loaded than the occupants for a "round the bay" charter.
More likely:
1. Lack of airframes / crews due to the disruption and mods required.
2. Airframe life - the airframe has a limited lifespan (this can be extended, but there will be an ultimate limit), and there is no prospect of a replacement type. If it is judged better for BA to keep Concorde flying well into the future, then they do not want to use up life on charters, particularly if they are not highly profitable.
NoD