There's shitloads of good items on dead accounts, if all of them suddenly come back just to sell out, prices will drop by 5 times.
But if they haven't sold out when they left the site, they probably won't sell now either, even if by some miracle they come back.
There are almost no good items for trade, if a lot of new people came they'd be forced to use really low/mediocre gear if they want to play
If this new player base wants to use good/high item, prices will go up like crazy... there's hardly enough gear to even support current players