> papers that lay the foundations for a whole field are usually very approachable. i'm not sure why this is

Kuhn talks about this in his works[1]. If I recall correctly, his argument is that when someone is creating a new field (new paradigm) there isn't pre-existing jargon to describe it in terms of, so it has to be described in accessible language.

It's once people start doing work inside the field that they start developing jargon and assuming things.

[1] I think it would have been The Structure of Scientific Revolutions, and/or possibly The Copernican Revolution