Here's the point you're missing. The overwhelming majority Linux users don't give a flying hoot about the average user or mass adoption. They just want a system that gets out of their way and let's them do their technical tasks. Linux succeeds and excels at this because it is precisely designed for that niche and curated by its end-users.
There are however people who do care about mass adoption, i.e. Canonical, "Linux Advocates". Generally they're either emotionally invested in Linux for some reason or they get a paycheck for their work. These people are the minority of Linux users.
Saying the culture doesn't care about design is absurd, it's the non-technical user we don't care about. Let's not conflate the two. Looking at a piece of software like XMonad or TMux it's hard to not appreciate the elegance in it's design. It's just different form of design that say iTunes or Photoshop.