I think 'make knowledge accessible' has too many interpretations to say that article complexity leads to a bad job of it.
I'm sure a Korean-Sengalese dictionary is very accessible, but not to me. A single page that gets every reader from A to B regarding the same knowledge/concept is rarely possible. It's a little reminiscent of Feynman's famous answer to 'How do magnets work?'.
I wonder if the author of the article had found https://simple.wikipedia.org/wiki/Main_Page before sitting down to write. If they're not simply engaging in wishful thinking, perhaps they actually want a fork of Wikipedia's STEM articles, with train tracks and mouse-over 'ELI16' definitions.
What I expect an accessible work to do is to explain things using terms that are as simple as possible. This does not mean to explain it like the reader was a child but, most of all, to avoid one simple pitfall:
Imagine you learn A, then learn B (which builds on A), and finally learn C (which builds on A and B). Now you have the knowledge to explain A more correctly and elegantly in terms of C, and you do so.
However, your beautiful and correct definition of A depends on C, which depends on B, which depends on A. So your reader has to understand C in order to grasp A and A in order to grasp C.
This pitfall has nothing to do with necessary complexity -- not avoiding it is simply bad didactics.
(2) Of course I can criticize their work, even if their effort is voluntary, and no obligation to help arises from that.
(3) I'm not demanding anything, I simply turn toward other sources.
If the intention of Wikipedia volunteers is to make knowledge accessible, they are doing an increasingly bad job. Letting them know that is a service, IMO.