One analysis I read by a marketer that makes good sense is that the speed was worth paying for LHR to JFK but not really on the return given the clock changes and speed.

Getting to NYC before the clock time you left London was a cool trick. It allows you to make a morning meeting in NYC without coming in the night before.

But flying subsonic leaving NYC after dinner and arriving in London for breakfast works fine. Getting to London faster in 3.5 hours travel time but 8.5 hours later clock time means losing a day in the air effectively.