That's not a functioning analogy at all, "their work resembles music in the way that Picasso's work resembles actual people" sound absurd. Music is not a portrait of "actual" music in any way, it's a tautology.
The Picasso angle is overblown too (as is his name and art, it is the convention), classical painting did not have a goal of resembling photo, and there's no artistic achievement in going as far from it as possible. Picasso's pieces have much more in common with classical portrait than classical portrait have in common with realistic image of a person, Picasso is nothing more than a minor stylistic branch of the same principles.
This whole take of Autechre being madly unconventional is a strange one, they practically do fucked-up pop music, with direct borrowing of hip-hop, electro, techno et al.
No music qualifies for the label music in most people's view, because there's no such view (for example, one of the most popular genres trap is trash to most people). And there's no such debate in mainstream institutes -- Autechre had a SIGN album interview on the main page of New York Times and their tracks are played on BBC radioshows both for popular and academic music.
Why is Autechre not more popular? People are generally not interested in musical intricacies of any kind, let alone this particular kind. Look up the fooking charts, it would be an insult to be among that. If anything, Autechre is unusually popular and successful for their type of stuff.