Because lost add-ons have a right to resurface, while most of the time its for the sake of attention grabbing "Lol I'm so cool look at me posting this thing that existed a while ago"; that doesn't mean the actual creation they are attempting to post is worthless.
People should not be discouraged to revitalize old add-ons or at the very least make them publically available. If an add-on is redundant (can be found in another topic) then simply locking the topic and placing a link to the other topic should suffice.