Firstly, most people are bad at writing. Writing is a skill so like all other skills it stands to reason that most people won’t be good at it. When it comes t

Firstly, most people are bad at writing. Writing is a skill so like all other skills it stands to reason that most people won’t be good at it. When it comes to people who are writing a dissertation, you’re looking for the intersection of people who are good enough at the other discipline to be in the position of writing a dissertation (presumably for a PhD) and are also good at writing, so it’s going to be a small subset of people who are going to do that well. Not saying these people don’t exist (Feynman is a famous example, but there are others). Secondly, writing a dissertation is hard. Technical vocabulary, jargon etc generally exists because it is a helpful shortcut to communication with experts in a particular field. So for most people, writing their dissertation such that it could be readable by a layperson would generally make an already hard thing harder and doesn’t add anything in particular that’s helpful to experts (if anything might make it harder for experts because they would need to wade through things that are redundant or unnecessary to their understanding) so you’re making it harder in a way that doesn’t particularly benefit you. Why do that?