Just getting a little historical perspective on this, jazz, in one form or another, has existence since the mists of antiquity. In Elizabethan times and well before that, people use to get together equipped with various instruments such as what was referred to as a "case of viols" (bowed instruments of various sizes), and "case of recorders" (same deal), a lute or two, and perhaps a cittern, perhaps a harpsichord or clavichord or both, and maybe even a Renaissance guitar (four "courses" or doubled strings)—and JAM.

They didn't call it that, of course, but that was what it was.

They usually had melodies to work from, and one or more of the instruments would be playing that, while the rest of the instruments would be improvising around it.

Jazz, the way it's done these days, usually improvises around pre-chosen popular or well-known melodies, and generally wanders far afield in a sort of "theme and variations" mode.

This sort of playing has been going on in one form or another for centuries.

I've known a lot of jazz musicians over the years and I've heard one helluva lot of jazz. The particular STYLE of jazz you're use to may be on the wane, but jazz—improvisation—has been around for centuries in one form or another and, by its very nature—and what musicians do—will continue to be around as long as people play music.

Since when have the Grammies been the arbiter of what constitute's a particular form of music?

Don Firth