My daughter taught me a Taoist saying:
"Beautiful words are not true, and the truth is not beautiful."
There are many reasons why government writing is not plain. Only one of them has to do with skill:
1. Confused thinking
2. Lack of critical thinking
3. Lazy thinking - you pass the buck to the reader to figure it out
4. Jargon has replaced standard style guide - e.g. "writing for ourselves then pretending everyone else should understand"
5. Legalistic approach - "give them all the raw data and that way we're not interpreting it for them" - and can't get in trouble
6. Executive preference
7. Public Affairs type "messaging" replaces substantive information or Public Affairs can censor
8. Unrealistic deadline or insufficient staff
9. Lack of collaboration, stove piping - e.g. "Stay out of my business"
10. Communication is one person's job vs. everyone's
11. Writing not exposed to broad audience for critical review
12 . Insulation from negative feedback
13. Worse consequences for providing bad news clearly than for muddling the information or making it less accessible
14. Clear communication seen as too simple - "Reads like USA Today"
15. Writing for professor of economics not 8th graders
16. Fear of misinterpretation, intentional or not; fear of negative press
17. Fear of getting in trouble or losing one's job for conveying bad news
18. Lack of ability to use visual aids when appropriate
19. Communication staff is operational rather than communication-focused
20. History or context of the information is omitted deliberately so as not to raise further questions
Plain language training is only partly useful to address the above. In fact one could argue it is a panacea used to divert attention from the real issues.
That's why PL is a law.