From the Description: "...In addition, we're going to stop this drop if it reaches 250 boxes, until we get confirmed shipment numbers."
Also from Mark's post: "A reminder that we're ending this once it hits 250 boxes, and we'll start it again (assuming) we get more confirmed numbers from our distributor. We don't want people signing up for box #305 and having to (potentially) wait 2 weeks to get their cards."