I think it's because Autechre simply doesn't qualify for the label "music" by most people's definition.
I used to dismiss that as a completely ignorant mentality, but I have kind of come around on that opinion. I love Ae as much as anyone, but their work resembles music in the way that Picasso's work resembles actual people. People who are used to, and expecting to see a classic semi-realistic painting of a person is going to be totally off-put by something like The Poet. As interesting a piece as it is, it resembles a person in the faintest sense of the term. About the only thing it has in common with a more classical portrait is that it is a bunch of paint on a canvas. There are vague hints of human-like features but you need to look to even see those.
Over the years I've realized that while my need for Autechre is rarely quenched by other music, my need for other music is rarely quenched by Autechre. They are separate mediums in a lot of ways. Autechre is where I go to for exploration, intrigue, novelty, and it benefits greatly from concentrated attentive listening.
On the flip side, if I just want to have something on in the background, or listen to something to cheer up or relax or whatnot, I'm much more likely to toss on something more conventional.