> many advanced areas of mathematics are inaccessible to most students because no satisfactory exposition exists
What is considered a satisfactory exposition also depends highly on the maturity of the reader. Not in the technical content of a specific area, but in the maturity of their mathematical reading skills needed for that area. This comes up a lot in algebraic geometry, where every student hits a wall when reading the central textbooks. The books are not necessarily hard because the author doesn't have a specialty in teaching and expository writing. Rather, the author is trying to induct the reader into a way of thinking specific to that field and the communication tools they use.
> I hope to see a change in the reward structure and system of values at research-oriented universities so that teaching and expository writing become legitimate as a specialty.
This is a problem in many fields. Teaching and exposition are often seen as low-value distractions from research, the type of work better left to "lesser" scholars (graduate students, non-tenure track faculty). Many mediocre researchers would be stellar teachers but you are more respected (and better paid) for research.
What is considered a satisfactory exposition also depends highly on the maturity of the reader. Not in the technical content of a specific area, but in the maturity of their mathematical reading skills needed for that area. This comes up a lot in algebraic geometry, where every student hits a wall when reading the central textbooks. The books are not necessarily hard because the author doesn't have a specialty in teaching and expository writing. Rather, the author is trying to induct the reader into a way of thinking specific to that field and the communication tools they use.