Black Vitriol

I am ready to craft my philosopher's stone and looking on the auction house for black vitriol, I have been finding that most of it is sold in bulk. I simply do not understand this. As far as I am aware, black vitriol is only used as a reagent for one thing, and one thing only - making a philosopher's stone. Since each alchemist only ever crafts one, and each stone only require 1 black vitriol, why would anybody purchase more than one? So why sell it in bulk? I see this item in lots of 2's and 5's every day for the last fortnight and have come to the conclusion that (i) either the sellers are a little loopy and wrongfully expect it to sell or (ii) the buyers are silly and purchasing multiples when only one is required. I guess if you need one, but only two is available, you will invariably buy two in order to get one.

The irony is that I every morning I search for it, I somehow expect there to be only a list of singles to buy. How silly am I...