Regarding Esoterica Penzance and Stonehaven, I believe there are several reasons they are literally gone in minutes (or less).
First, unlike some online retailers, Smokingpipes has the integrity to not charge inflated prices on their limited inventory.
I've watched it unfold in real time. They list one variety at a time. Tins and bags separately. They usually have a one tin or one bag limit. In spite of that limit, they sell so fast that if you manage to get one in your cart, you need to checkout immediately; otherwise it won't be available by the time you complete the transaction.
Technology is a factor too. I've seen other sites brought to their knees by Esoterica drops. Smokingpipes' site just keeps chugging away, enabling the sales to continue to fly through.
Finally, Smokingpipes is quite simply the largest retailer of pipe tobacco, probably in the entire world. They get more people trying to buy their inventory. I bet the employees dread Esoterica drops.