...you should probably check out the recent (2003) NEA-funded report on the worklife of jazz musicians. You can get it here. Scroll down and download the PDF of the Executive Summary.
Right there, in the introduction, I finally saw in writing exactly the thing I've been struggling with over the last four years with the IJG. I quote:
"As A.B. Spellman indicated in his introduction to the NEA publication American Jazz Masters Fellowships 1982-2002, jazz was 'built on the discipline of collective improvisation ... which allowed for maximum expression of the individual within the context of the group.' The group, however, is often an ever-changing one. Unlike classical music, with orchestral members staying together for decades, or even rock, where more often than not musicians make their music as a group, jazz musicians often look for jams or gigs as individuals rather than in groups."
"Playing with multiple groups can be problematic. Musicians may not stay in a group long enough for it to grow into a solid band, and moving from group to group and gig can make linear career development difficult."
Yes... for both musicians and bandleaders. What you end up with are fewer cohesive, innovative groups, and more pickup groups that get together ephemerally to play--what else?--standards. Think about it: how can you pull off something Mingusian, something Ellingtonian, in a session, in a weekend, even in a tour? Those guys had more or less regular working bands which, though never entirely consistent in terms of personnel, were together long enough to push each other in some concerted but fascinating new directions.
Anyway... everything else you might have assumed about the extra-musical aspects of jazz is borne out by this study: in particular, most of its musicians are highly educated, pathetically underpaid, and lacking in health and retirement benefits. All this in the face of jazz being identified as a "national treasure" by the US Congress. Dontcha love the irony?
(Thanks to Robert Jacobson for forwarding this to me.)