They can, that's how the Concorde used to fly, but it meant that a flight from London to New York was only able to be done at supersonic speed for something like half the trip (measured in time). The aircraft was also incredibly inefficient at subsonic speeds because the aerodynamics were all optimized for much faster flight
I am just wondering because NY-> LON is mostly ocean as is LA/SFO -> asia/australia coast where big cities are. Intra-continental flights like NYC->LA are a bit long for sure but most pain points are international and between coastal cities.
So you're saying instead of cutting down 8h trip to 4h it would be more like to 6h? Still something imo.
Because being over an ocean isn't good enough. It needs to be in a location that will not bother people with political influence