Somebody once wrote "Jazz is the sound of surprise" and going to a bar to hear a quintet of two horns, bass drums and piano play head-solos-head on a string of tunes either introduced between 1940-1960, or newly written to sound like they date from 1940-1960, isn't a recipe for being surprised.
I think you make a good point. But sometimes jazz can still be surprising, especially if it is done really well. I remember one particular evening sometime in the 90s when I walked into a bar in Brussels with some friends, and there was a band playing a bunch of Ornette Coleman arrangements. I am not generally that much of a fan of jazz, but it was just so well done and the harmonies seemed so fresh and interesting that we all agreed to stay and listen till they had finished.
There was also a very modern jazz ensemble in San Antonio before I left in 2010 that played a lot of original compositions with polyrhythms and odd time signatures that I simply found fascinating. They played so fluidly that a layman would never suspect anything odd about the time, other than it was infectious.
I think the problem is typically you have a rhythm section playing the same old changes and a couple of horns blowing solos, and there really is not a lot of composition or structure. After a few minutes it all starts to sound the same unless you have really phenomenal players.
I remember walking around at a music festival I was playing at. A jazz combo opened up with a medium swing tune at the first stage. We listened for a few minutes, got bored, and walked down the street to see the other stages. We got back about 40 minutes later and the band was playing another medium swing tune. Of course the chords were different, but the tone, texture, and rhythms sounded exactly the same as they did previously.
This is a problem even with highly skilled musicians to some degree. You have to be very sophisticated as a listener to pickup on the nuances, which often amount to note choices in the solo, because so much of the "sound" of the music remains constant from tune to tune.
I think it's a lot more interesting if you have more than one horn and they play in harmony together and the brass instruments use mutes to change the color of their tone. But as players, the focus is often on how athletic and technical you can play, so the audience may not get a lot of lyrical content to draw them in. To the untrained ear, an incredible solo can sound like a bunch of random notes. In other words, it sounds like noise.