2 years or so ago I put up a question in AB Suggestions, as there were over 500 "unanswered questions" in Q & P, and it was taking ages to load then!
I suggested they delete the really old ones (some were already 2 years old then), and AB Ed said - good idea, she'd get the tech guys to look at it.
I looked again a couple of days ago, and there's now over 2000 unanswered - some of which are just people saying thank you for an answer given, so they appear as unanswered, but they all just slow the site down.