Same reason putting Ascii characters in my titles mattered to other people, it's annoying. I think most people would want to read the thread to get information and updates on the mod, not be notified each time someone adds their name to the list. You use the same method, hence the tag. Makes it hard to follow your threads as well when the flurry of posting takes place for list signups. Then the repeated "look back on page #### where I put myself on the list" ad nauseam. In this day and age we don't have a better way to let people sign up, in order? A google form would easily give the same functionality without the repeated, unnecessary posting.
Not to mention the repeated "add me to the list" when there is no list to add to. After you've closed the lists, etc. It's just not a great way to manage this kind of thing.