It failed because trading slightly shorter flight time for much higher cost was not worthwhile. Instead, airliners have been optimized for cost reduction and efficiency at high subsonic speeds.
I am aware that airlines today fly slower than 50 years ago, to improve fuel efficiency. That said, all orders except the British and French flag carriers' were canceled because of the overland bans, correspondingly greatly increasing the per-unit cost of those that were sold. I think the NYC-to-London/Paris routes were (slightly) profitable; were there no overland bans, are there really no other routes that Concorde could also have flown?
