It seems like a (rough) calculated loss strategy. Return shipping one of something, then relisting and shipping again, may have no profit.
On the other hand, someone who got greedy like
frampton (and I am not faulting that, I too might have ordered as many as I could find if I had seen that topic but I didn't), may have enough product that it makes sense for amazon to pay shipping to get them back... just speculating that they've done this before many times and are an efficient monster that has crunched the numbers and knows what their cost vs customer retention rate vs customer valuation is.
Sometimes, cold hard analytics done by a computer, err on the side of subjectivity in their fairness, but at the same time, if I did what frampton did, and it seems like something I might have done if I had that info at the time, I would have felt like I was playing the lottery and would have expected a rough road when that much money/loss was at stake.
I'm not excusing them from shipping the quantity stated on a listing. That is a primary part of the contract between buyer and seller, but the old saying goes that if something is too good to be true, it probably is. Buyer beware, the era where a seller has to honor their listing has unfortunately ended.