If a wrestler is not on your Sectional roster submitted by your AD, he can not be entered. Also, if no wrestler is entered at the weight class during the seeding meeting, then no wrestler can be entered later.
If they did enter a wrestler, the new wrestler can be entered as a replacement. If the entered wrestler was a seeded wrestler, he is removed and new entry is placed in the #6 seed and everyone moves up. If they are unseeded, then they are entered as if the were the original wrestler.
An advantage of not submitting a deserving seed is to remain separated from a higher seed. Seeds 2,3, and 6 are opposite of the #1 seed. This would be one reason I could imagine this would be done, not sayin I agree with it either, just trying to answer your question as to the why.