Shaving off enough hours to be able to board a plane in the early morning, have a two hour business meeting in the destination and fly back and arrive home in the late evening of the same day is a huge draw to some.
BA001 LHR 10:30AM -> JFK 09:25AM
BA002 JFK 08:30AM -> LHR 05:15PM
AF002 CDG 10:30AM -> JFK 08:15AM
AF001 JFK 08:00AM -> CDG 05:45PM
That's why flying westbound supersonic is less of an advantage. Because as you can see, flying west, your day is still wasted, even if you leave early.
And realistically, from your plane at JFK to Manhattan, that's got to be a least an hour and a half (immigration and cab/limo). And assuming you'd have to be at JFK just an hour before your flight (and for an international flight that's ballsy), plus with transportation still taking an hour, you just wasted 3.5 hours commuting forth and back to the airport.
That schedule wouldn't work unless you flew to Manhattan. And even then, it'd be tight.