I made no such universal statement. Some people enjoy hard things simply because they are hard. My claim is that this can also result in people thinking some literature is better than it is, because people draw satisfaction from the effort itself.
The point you might be missing is that some people might enjoy hard things not only because they are hard, but because only through their laborious efforts is the true brilliance of the work revealed.
For me it's not even that, it's simply that The Brothers Karamazov and other novels like it have historicity and depth to them in a way that modern-style light popcorn novels never do. The hardness therefore is more incidental than the means to an end in itself.
And for what it's worth, there's plenty of modern-style "hard" novels that I've enjoyed immensely as well, including House of Leaves, Infinite Jest, Shogun, The Pillars of the Earth, and [pick any Neal Stephenson novel published this millennium].
Your initial premise: "I find that literature that requires work does not provide more food or insight into the human condition..."
Your conclusion from this premise: "If complexity is not what makes the work valuable, what purpose does it serve?"
And you answer your own question with a cynical take: "I posit that for some people complexity for the sake of complexity _is_ the appeal."
This makes me want to kick myself for reading Hacker News to be illuminated about the arts.
Still, I love user lermontov!