I've often wondered if the big manufactures see a potential market in super sonic travel, or if they see it as too risky. Is the safer option just to continue with small steps and improved fuel burn of 5%-7% each model?
As several people above have noted, the fundamental problem is that supersonic flight is very, very expensive, and the potential market is just too small to justify the inevitable costs. If it was such a good idea, then where are the private supersonic jets?