The publishing industry is a very old one, which means that over the years the people in the industry have established procedures and guidelines meant to streamline the process of getting from book idea to print. Of course, such establishment works best in a static world, as can be seen by the frantic response to young publishers breaking the rules, creating eBooks, and setting low prices.
We have rules for grammar so that someone can know a language and understand books written to those grammatical rules.
One would think that an author would be capable of reading submission guidelines which were written in their native language, and follow them. Of course they could, but why do so many editors complain about submissions that do not follow the guidelines?
I think it is because the editors themselves have fallen into the trap of convention in the publishing industry. Everyone has "Submission guidelines" so they think that they must need them, too. Yes, it would be good practice to set rules for submissions, so do just that. Do not set guidelines unless you expect them to be read as helpful hints.
If you want to be forceful and reject submissions that are not within your standards, set standards instead of suggestions. How about using "Mandatory submission rules (not just guidelines)" to properly cast your requirements?
Can you be bold enough to not use old industry terms that apparently do not carry your intended meaning? What would be a new term that would properly convey your meaning to the thousands of authors out there who do not know your business?
This is your industry. Define it.