They want the end time for sniping which ends up getting the auctioneer less money.
It is better for the auctioneer on forums to give a vague end time. Let's say between 6am and 2pm on x date.
This forces the bidder who truly wants the item to fight for it monetarily, as they have no clue when it will end.
None of my auctions have ever had an end time listed. I don't want reselling cowards to wait for the last minute to bid. I want people who actually want the item to fight for it, if a reseller wants to fight for it as well that's fine but I always give myself options with the rules of my auctions.