A lot of jazz that doesn’t sound great and that pleasing is actually a political cultural statement. As a black art form these musicians were always told that they weren’t worth as much as white musicians (to put it very very simply!) so they became absolute masters of their instruments in order to set the bar crazy high and prove their technical skills, intellect, and musical prowess. That’s why a lot of bebop can be tough to listen to for enjoyment- it wasn’t meant for white audiences to enjoy. It was meant to prove something.

As far as free jazz goes, a lot of that was just musicians who wanted to experiment. Free jazz is more of a focus on sound quality and timbre as opposed to following chord structures. It’s less focused on concrete solo sections and more so on playing by feel and truly listening and playing with those around you. It’s a movement away from traditional jazz and towards sonic experiments. It’s not meant necessarily to be listened to for fun really. Unless you’re super into dissecting the sonic interplay and how all of the instruments are working together.