All passenger jets have pressurized cabins, but they are working at lower pressure differentials than what you need above 60k feet, and they sometimes fail, wit

All passenger jets have pressurized cabins, but they are working at lower pressure differentials than what you need above 60k feet, and they sometimes fail, with oxygen masks being the fail-safe. If you go above 60k, and the plane experiences a rapid loss of cabin pressure, you have 60 seconds to restore cabin pressure before the passengers start dying. So the failsafe system will have to be massive. That increase in weight and complexity isn't worth the efficiency gains. You mention Concorde, and indeed it had a very substantial failsafe system even though it only touched the lower end of the limit. Concorde had really small windows, so even with two windows gone it took some time to equalize pressure. The pilots had positive pressure oxygen masks, and the plane had the ability to drop altitude immensely fast in an emergency.