The times I have seen this in the past is when a listing violated
ebay's terms and they yanked it after the fact.
From a buyer's perspective it's extremely annoying as the listing just evaporates other than being a line item in your buying history. If you deleted any emails associated with the purchase, you're SOL. Even then, if there's any problems with the item, there's no listing to refer back to. No pictures. No text. Nothing.