Meno, it really was that simple. The US Mint had made only a limited supply of certain coins and the demand from them was greater than the quantity. And there is a two quantity purchase maximum per person permitted by the Mint’s website. They sell out within minutes of going on sale on the US Mint website and have an immediate premium resale value.
That said, I don’t see anything wrong with offering folks to buy it and paying them a premium that doesn’t represent the full market value.