eBay bid retractions

[swarmee]

So the guys on Blowout have mentioned that this should at least minimize the risk of "bid shielding", the process where an expensive item can be won cheaply by two bidders colluding with each other. For example, a $1000 has an initial bid of $100. Bidder B bids $2500 on it. Bidder C bids $2600 on it. At the close of the auction, bidder B retracts their $2500 bid, and Bidder C has the leading bid with only a $105 bid (one increment over the initial bid). Time runs out on the auction.
I don't think it's a widespread problem, but I have read about it happening a lot more with the basketball snearkerboi price runup over the past year or two.

But my real question is, "Why just the sportscard category?" Guess all those ice cream collector shill bidders can still retract, right?