Your description of the need for anonymous posting is so well-worded, I really do think that would be the perfect way to describe the importance of anonymity in the meme's guidelines. Constantly signing your name to comments/fills/prompts certainly encourages favoritism and it really isn't fair on the rest of us.

Yes, it's not the worst crime in the world (and people are welcomed to link to fills on their AO3, FFN etc.), but it does upset other fillers to see somebody being showered in comments/attention all the time because they're demanding it and ultimately these fillers are going to leave and go elsewhere.