Closing doors due to a severe case of misoneism or misocainea (fear of the new) only limits. Here here for expansion!
It has a lot to do with social anxiety as well. Whether people admit it or not, a lot of the time musicians lose sight of the dividing line between their social standing and their tastes/repertoire.
I'm in no way above this tendency. I've played in the local rock scene for years, and every time a new song is being worked on, myself and the musicians I work with have to come to grips with the idea that a rock audience is very difficult to cater to. When you think of how competitive the overall scene is, you have to realize that, as fun as it may seem, nobody's going to care if you go up there and play ten tons of complex music with really unconventional structures. True, sometimes bands get to do things like this (like Frank Zappa did), but there's always some level of catering to the demands of the audience. But that's the rock music scene, an environment that I would argue has no hope of fully divorcing itself from its nature as
art/entertainment. Classical and jazz have pretty much broken off from their original ties with popular culture and have both become self-sustaining artistic communities. Within those genres, tons of composers and performers have clearly made the decision to disregard convention and try new approaches to realizing their artistry to the fullest extent of their imaginations.
Again, it comes back to the educational environments. What I just described about what I see as the prime movers of the independent classical and jazz communities is very often counteracted heavily by the programmes and teaching methods of music schools and private teachers everywhere. A heavy amount of the social anxiety wrapped up in musicianship is obviously a result of the way high schools (at least in America) treat everything. Music = marching band, school orchestra competitions, school choir competitions, conditioning one's self to try out for all-states whatever, after-school jazz-band, and yet more competition in the annual battle-of-the-bands). From the get-go, everything is about playing well in the group. Very few schools offer theory courses and when they do, they spend the whole year preparing for a standardized AP test and no time at all on composition, creativity, or anything that requires individualistic drive. From what I've seen, college programs take this and raise it to the power of 10, creating a massive schedule of rehearsals, courses, extra courses, and leaving little to no time for individual pursuits. Of course, real genius musicians will find ways to circumvent this drudgery and blaze their own path. They always have. I would argue, however, that the drudgery-loaded schedule does a horribly good job of sapping a lot of peoples' potentials as trail-blazing individualized musicians and spits them out of the system as simply well-behaved and jaded musical conservatives who ultimately never make an untoward blip on the radar.
Getting back to taste...a lot of these musicians end up hanging out with nobody except other musicians, most of whom are taking similar programs, playing in similar groups, and attending the same boring music history lectures week by week. Since the music itself is by-and-large a form of drudgery, most of them aren't interested in talking about too much music from outside the prescribed circle (and usually the social interaction is simply geared towards sex, drugs, video-games, and garden variety bullshit). Every time I've sat down with a group of music-school kids and started yacking about composers I like, etc..., I just get a sense that everyone's not only completely tired of music, as is often the case, but also that they are totally disinterested in hearing about anything outside of the stuff they listened to in high school (before they started hating music). Usually that's socially-accepted-yet-painfully-out-of-touch crap like ska music (as I've often encountered in conversations with trombonists and sax players) or jamband crap (which everyone my age was guilty of fawning over in the late 1990s even though the only real reason people cared about it was so that they could smoke weed with their buddies at the show). When classical is involved, it's always the "who?" game unless you luck out and mention a name associated with the player's assigned repertoire. I knew a drummer who played an Albeniz piece arranged for mallets as one of his recital pieces. When I asked him about why he chose such an interesting piece, he said something along the lines of "um....oh, that Spanish crap....that's something my teacher told me to play. I have no clue who the composer was" The performance was very strong technically but incredibly uninspired. I went to another percussionist's recital a few weeks later at the same conservatory, and he cranked out the same piece...just as mechanically...and similarly couldn't carry on any amount of conversation about Albeniz or anything about the piece itself. All I sensed was that these guys were pretty much just doing whatever it took to make their teacher happy and investing little to no real joy in the pursuit of a letter grade. What's even sadder is that nowadays, both of them are just puttering around, drinking too much, occasionally teaching a private lesson or sitting in at some performance with a former acquaintance, and preparing for long, hard careers in the service industry.
Topic: why modern music is hardly accepted by audience nowadays?