Not sure what the question is. You mean someone else has bought all of these, how can you tell? Only the first one, which was an auction, you can see the bidding, the rest of the BIN listings you can't see who bought it (or I can't, maybe you can?).
As to their motivation? Dunno, some people collect weird things, or maybe they've got a project in mind. Or they're trying to corner the market and buy them all cheaply to force prices up then sell them for a profit later.
I've got one in OM mount that I rarely use, anyone want that for $300?