I think it is important not to boil fiction down into the 'idea or set of ideas the writing expresses' because if the author could so well articulate their 'idea' then wouldn't they be better off writing an essay rather than a narrative?

Instead, I think the fascination with difficulty is exactly this -- the idea that some ideas are amorphous and difficult to express directly, and that authors have tried (successfully and less so) drastic measures to try and, in their own way, do exactly what you said in your comment.

And there is something, for some, inherently interesting in the different contortions of text that experimental writers have come up with.