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
It required a lot of blind playtesting and learning how to watch people while they were reading to figure out what was good and bad in the rules.
You get or lose players in the first five pages or so, and almost definitely by page 10. If players can get get a running start on what the game is all about—if you get them a solid context to work with—they’ll have hope, even if your game is complicated.
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.