We certainly haven't seen huge leaps in fuel efficiency of aircraft in the last 50 years.
That is not true. Modern airlines are 20-30% more fuel efficient than the original 707. While not an orders-of-magnitude change, it's significant. Physics is a bitch.
The 747, introduced way back then, is still produced.
Because there is a business case for the plane. It has little to do with technologic improvements. Other planes have come and gone mostly because of economic issues.
We had rockets that went to the moon, but no longer have the technology.
We have the technology, just not the political will to spend the money on this particular endevour.
We had reusable shuttles 40 years ago, but no longer have them.
A combination of money and the fact that the Shuttle was a hare brained design, even if it was really cool.
We had Concorde, and only now someone is trying to recreate a smaller version of it, and who knows if it will even get to market.
And again, it's the money, honey. Not the technology.
We had bombers that whose lifespan was, well, 60 years and still counting, while more modern bombers have come and gone
Blame that one on the idiots in the Air Force and in Congress who couldn't get a hammer built in a cost efficient manner. The physics, and therefore the basic design, of planes has been well understood for some time. Materials, electronics and engines have all improved drastically. And guess what. The B52 has all sorts of new materials, computers, engines.
Let's face it, as far as transportation goes, we have de-innovated. Yes, computers have gotten faster, and the gadgets in cars, trucks and planes have improved, but the transportation systems themselves? Stagnant at best and losing ground in many ways.
Not really, it's all about the economics (and the greed and stupidity of the military-industrial complex). We aren't 'de innovating'. If anything, we're getting smarter (except the military). We aren't pretending that the world is a Jetson's TV show.