The true nail in the coffin was the development of the lie flat business seat, which meant that you could cross the Atlantic in three hours in a plush but cramped seat, or spend less money to sleep for six on a redeye and arrive well rested. At that point three hours was not a compelling enough time savings, but the Concorde also didn't fly far enough to do routes where the speed resulted in more significant time savings, like on transpacific routes.