Originally Posted by BookMouse
There is a psychology to the choice between the words 'guidelines' and 'rules.' Guidelines are there to provide suggestions but you can ignore them if you want where rules are there to be followed, or else. Breaking or ignoring a guideline isn't much to ponder whereas breaking a rule requires a more conscious consideration and, if you were taught well, a critical analysis of 'is this better or more proper, why, and can I defend it?'
I think it's also because so much of amateur writing is simply *awful*. I consider myself an above-average writer and the first short story I ever had published online was a real stinker. The rules are presented as rules because so many beginning writers will do much better following them (and provide less headaches for their teacher/editor/reviewer/whathaveyou).