Having an immense number of items listed on a website at a particular moment in time is one thing.
Trying to find that actual physical item amongst FOUR MILLION items scattered over mutiple storage facilities is quite a task , and given that any one of them may have been ordered by multiple potential buyers over the course of the week between the sale starting and the orders starting to be processed then it's easy to see how stuff can be 'out of stock' by the time another order for said 45 is sent for picking.
I doubt that many can actually visualise just what a million actually is , it's a word that's bandied about so often.
If you start counting right now , 1,2,3,4 ... etc , one a second , every second , non-stop , it will take you eleven and a half days to get to that million mark , so forty-six days to get to four million.
You'll all be bleating next that he has no upcoming auctions after next Wednesday.