Why is Concorde no longer in service?
The crash was only one of the (albeit an important) reason for the grounding of Concorde. Actually, the aircraft was retired around three years after the crash. The main reason was that not enough people were flying it to keep it profitable.

The Concorde as a technological marvel, but it had a number of disadvantages:


The aircraft was costly- The program cost over $3B and produced 20 aircraft, of which 14 were used in commercial service.
Maintenance costs- The small number of aircraft and technological sophistication meant that the cost of spares was high and options limited.
Operating costs- The Concorde consumed nearly three times per passenger fuel when compared to the Boeing 747-100. Still, the aircraft made operational profit due to the high cost of tickets.
Recession- After 9/11 attacks exacerbated the global downturn in aviation due to recession, there was an enormous drop in first class air travel, on which Concorde was dependent on.


While announcing the retirement, British Airways cited


  commercial reasons, with passenger revenue falling steadily against a backdrop of rising maintenance costs for the aircraft.