Google Boeing Sonic cruiser for the whole story why; bottom line is airlines don't want to buy it as they don't think there is a market -- most pax want cheaper and not faster and won't pay even $1 more. The Concorde sold 16 planes even though it was a tremendous technical success. Boeing decided to build the 787 instead using the Sonic cruiser technology (and cruise speed slightly faster than current planes it is replacing, but >10% slower than the Sonic Cruiser -- but with 20% less fuel consumption).