I'm guessing it's there to persuade people that have preconceptions about lisps verbosity/readability to read the article instead of immediately dismissing it.
What's truly orthogonal is some notion of "expressiveness" or "teachability" or otherwise being-able-to-read-and-understand.
The example that you should think of here is mathematics papers. The ideas are stated in their clearest form, which usually is absurdly brief: lemma, theorem, proof. You can then spend about an hour poring over each line to figure out what the heck it's expressing, before suddenly a moment of clarity dawns on you and you see all of the connections together.
Why would they write incomprehensibly? It's not because they don't want to be understood; these are peer-reviewed journals we're talking about here, and someone else must read and OK your work. But it's because when they make the fewest assumptions and the most broad argument, their work maximizes power and usability and robustness.