Not trying to play the authority card, but I am an Aerospace Engineer by training. First thing first Concorde was a marvel of engineering and quite a bit ahead

Not trying to play the authority card, but I am an Aerospace Engineer by training. First thing first Concorde was a marvel of engineering and quite a bit ahead of time as someone mentioned in the comments below it ultimately boils down to economics, per-flight cost was enormous. Concorde effectively gave a 6-hr gain on Trans-Atlantic flight. You need to spend a lot of fuel to fly supersonic , even Concorde had an optimal sub-sonic cruise-point around Mach-0.98. And It was allowed to fly supersonic only over uninhabited areas (read Oceans).If you google around specific-fuel consumption charts for various types of engines against mach number you'll know what I mean.(Also try to search for specific Impulse characteristics for a feel for efficiency over a mach number range)