It's all well and good saying that the choice to buy in bulk or individually is there, and that demand will cause sellers to list items in smaller quantities at higher prices for the convenience.
However that relies on the sellers recognizing that demand and catering to it.
If no one is selling these things individually and everyone who wants them individually is being forced to buy in bulk (and get screwed over for it) then that demand is never going to be recognized.
The option to negotiate these things and inform the sellers of a certain demand simply isn't there, so this system doesn't work.
I mean, imagine going to a videogame store to buy FFXIV and being told "sorry, we only have stacks of 10 for $300 available", and the store clerk has no authority to change this set up and upper management have no contact details. It's insane.
What would work better is some kind of adjustable system, whereby you can list multiple items at an individual price, then set your own discount price for a bulk buy.
E.g.
Individual Price: 1,000g
Multi-buy discount: 5g/unit
Resulting in....
Stack of 10: 9,950g
Stack of 99: 98,550g
(although in this example 5g per unit is probably too little to work)
Then people can purchase your items individually if they wish, or in bulk for a discount, and everyone is happy.