Imagine if the artwork for every boardgame was created by the designer. All of the cover art, cards, boards, etc. I imagine there would be a lot of complaints about the quality of the artwork. Expecting untrained designers and developers to write professional-quality instructions is just as unrealistic as expecting them to do the graphic design.
Quotes about writing game rules
I think the rules are of paramount importance. Your main goal as a rules writer should be that any group’s first game (guided by your explanation) should go off without a hitch. If the rules are unclear and certain rules get botched the whole experience can get botched. And we all know what people say about first impressions.