Some scholars feel that if their prose is too clear, they won't be taken seriously. There is a gravitas in being a little difficult to follow. Even undergraduates try this. The real trick, however, is to explain complex ideas clearly and concisely. Write in a way your uncle could understand, but with no sacrifice of complexity or nuance. I'm not there yet myself.
Clarity is also luminosity, radiance. Your ideas should jump off the page. As I said, I'm not there myself.
It does no good to say "write clearly" as abstract advice. The way to achieve this *stupid* degree of clarity is two-fold. Emulate models of writing that exemplify this trait; break down what these clear writers do. Secondly, read your own prose from the perspective of your aunt, your cousin, your neighbor. What don't you understand in your own writing?
Ok, no I know you're going to say that there will always be a need for a technical language specific to your field. That is not what I'm taking about here, though. Very little--maybe 10%--of why your uncle or grandmother doesn't understand what you're writing is due to your use of terms like catachresis or chiasmus. Most of obscurity is due to syntax, or to technical vocabulary USED INCORRECTLY and MISLEADINGLY.