The reason (the only reasonable one o can come up with) is the added cost of inspection before selling them.
I don't disagree that the mark up mentioned in the post was extreme, but I don't have a good idea of what it would be otherwise.
Based on my having visited places with high tariffs, or a difficult place to deliver things (top of a mountain) you definitely see large markups. Not 6x, but 2x-3x isn't uncommon.