system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why has aircraft technology (seemingly) stagnated in the past 30 years?

I'm sure that things like radar and black boxes and other smaller things are going to always be improving slightly, but aeroplanes in general seem to have stayed the same for many years. If you look at 80s movies, the 'heroes' will be driving noticeably old cars, using phones in booths, and everyone's clothes are different, yet planes are the same. In 1979 I'm sure that 20 year olds would have thought by now that we would all be flying in concordes, but that obviously isn't the case. Why haven't there been any large recent advancements in aeroplanes?
gpt
On top of all the current comments:  
It happens to be that the current lineup of aircraft design-wise is the pretty efficient (aerodynamically, and therefore economically) for its given purpose (travelling large distances).

There have been changes to aeroplanes since the 80's but most of them aren't immediately noticeable from the outside. For example the use of digital controls (fly-by-wire) replacing mechanical controls in the cockpit, changes in the aircraft body composition (stronger, lighter), engines being quieter and more fuel efficient (787 dreamliner being the best example).

Concordes fell through because it was more or less a premium novelty experience, until the fated crash occured which tarnished the reputation of supersonic commercial aviation in the public.

There's also a lot of bureaucracy that happens when you try to implement a new design, all kinds of regulations, safety thresholds and whatnot. The A380 being an example forced several major airports to widen runways to accommodate for the increased width/wingspan of the aircraft.

All in all, the airplanes in service generally 'work' at some level of satisfaction, there hasn't been a technological breakthrough in aircraft design which allows greater efficiency in transporting a large amount of passengers, and as such the status quo is established.