Maybe because it wasn't flagged as an ME by the vendor, and only some bidders realised what it was. Of them, perhaps not all were 100% sure and so gave up more easily when the price started going up.
ETA: Yes it does seem to be true of most high end coins on e bay. They usually go for a lot less than at a standard auction. For example, I got my 1895 2mm in a/UNC for just £231 in 2012.
As for the forces at work, I'm not entirely sure. Maybe standard auctions such as LCA, dnw, Spink etc, attract a wealthier and more international clientele. Not saying that is necessarily the prime reason, but it may be one reason.