I agree with most of what you wrote here. One point I would like to add though is that there were massive amount of military investments that went into plane de

I agree with most of what you wrote here. One point I would like to add though is that there were massive amount of military investments that went into plane development during both world wars and the cold war, allowing complete new features. Also, it's not like no ones tries to bring new technologies on the market. But the number of planes sold is nowhere near the number of cars sold, for instance. So new investments are pretty risky. Look at the Dreamliner or the A380... Both delayed and still with major design issues. In the general aviation, a European motor maker introduced diesel motors for plane, which allows a much lower mileage, and an economic flight of even 2-props planes (see DA-42). There were so much technical issues that the company got bankrupt. It's not a compelling argument for new customers tempted to buy such a diesel plane. When you buy a plane, you don't want the company to go bankrupt in 3 years, so you take a Piper or a Cessna, even if these are massively inefficient. Finally, look at a C172 glass cockpit. The outside design may still be the same as it was 40 years ago (as is the motor, almost), but the cockpit is totally different, with brand modern software, complex GPS & autopilot capabilities, etc. Flying has become quite different in the last 10 years because of that.