Supersonic Flight - Why we don't travel that fast

We have been able to travel at supersonic speeds for decades, the technology is well know as are the consequences of going very fast.  There used to be Concordes but nothing after them.  What happened, why don't we do air travel at supersonic speeds (at the moment) and why almost all commercial airplane travel is in a sweet spot of about 0.85 Mach (speed of sound) at an elevation of 35,000 - 45,000 feet.