Whatever the reason for why people can't write, I agree it's a big problem.

I've found from experience that if I write to colleagues using jargon that they don't all necessarily understand what I'm saying or some accuse me of omitting essential detail. When I try to remedy the problem and rewrite using simpler terms then I'm accused of stating the damn obvious and or being prolix.

It seems to me that there is no satisfactory answer, that is unless one has the good fortune to be a member of that very small and gifted group who can write both succinctly and clearly.