We’ve revolutionized the way that we travel in airplanes by changing the materials we build them with, the engines we put on them, and the general dynamics of how we design the airplanes. The question that still exists, why can’t we make them fly faster?
The short answer, physics. More specifically what’s called the “Area Rule,” this rule defines how much drag a plane experiences at transonic and supersonic speeds. The most important thing about an airplane and how it operates is how efficient the plane flies at cruising speed, usually mach 0.75 to 1.2. In general the faster that you go the more friction the air around you has and adds to your drag. This is why it’s incredibly hard to maintain supersonic flight over transonic speeds.
Overall this rule dictates the way planes are designed to be able to give the optimal speed while flying through the air. Long ago we had ambitions to make supersonic air travel the future, but instead with high oil prices the more efficient and money saving way is to operate at transonic speeds with an optimally designed aircraft to fly through the air with the least amount of drag possible. This is mostly why Concord and other supersonic aircraft were retired in the early 2000s.
