Whenever I'm at the airport I wonder two things: why can't they invent teleportation and how can airplanes still be so slow. We've been flying for decades and air travel hasn't gotten faster. Why the heck is it still slow?
The big answer: fuel. As in, if you fly too fast, you'll burn too much and it will cost too much monies. Commercial airlines would prefer flying at a specific speed that enables them to be as fuel efficient as possible. According to Slate:
By the laws of physics, the increase in drag equals the square of the increase in speed, so even a slightly faster flight requires a lot more fuel. Hiking a plane's velocity by 10 percent takes 21 percent more energy. Speeding up by 40 percent approximately doubles fuel consumption.
It's crazy. Flights are actually longer now than they were back in 1983 (NYC to Denver is 19 minutes longer) and even 1973 (DC to Miami is 45 minutes longer). It's probably safe to assume that airlines have found the perfect speed to maximize fuel while not sacrificing too much speed.
The littler answers to why air travel hasn't gotten any faster is because there are more jets in the air now. Jets, unlike propeller planes, fly at the same altitude as commercial airliners and when a commercial airliner is behind a jet, big boy has to slow down. Also, airlines have gamed the system on reporting flight times through block padding. They've add a few minutes to scheduled times in order to make it seem like their on time (when they're not). It's all screwy!