So why is jazz not as popular as it once was? I think it's mostly due to hip-hop's rise as the preferred authenticity-signaling genre for many white listeners.There was a brief period in the '70s and '80s when jazz music worked it's way into the mainstream. Audiences embraced quite a few prominent and important artists and supported the genre through the purchase of LPs and then a horde of CDs when that format brought a tremendous number of titles spilling over into the mainstream. Guitarists, especially, found audiences during that era.
Jazz has always fared well among musicians and people who like to attend closely to creative expression, formal innovation, complex musical structures, improvisational heroics, and the like. But for a significant part of the 20th century, jazz was also a popular way for whites to express enthusiasm and support for blacks and black culture, and to distinguish themselves from other whites. Someone commented: I know I should like jazz because it's cool and important …
Sting, and his Dream of the Blue Turtles album, was a kind of watershed moment. Sure, people hated it, but a lot of people were exposed to musicians who would have never been heard by his audience.
I think the real answer has to do with the fact that nobody buys music anymore. And if nobody's buying it, nobody's making it, either. So, there are fewer and fewer jazz albums that people are going to be exposed to (and listen to on new technology platforms, like Spotify) even though the genre continues to crank out titles.
People will always pay too much for authenticity, but what used to socialize people with the music they buy was the exposure that a jazz artist could get from in-store album plays and by occupying the part of the music store where the "cool" stuff was housed.
Jazz is just another victim of the idea that music has no value and should always be free.