Some items move slowly because there's almost no reason to buy them for example. The only new found reason is spiritbond fodder and an economy can't be supported on spiritbond fodder. This is why I actually liked FFXI's itemization because as you're leveling there's always going to be the useless pieces of gear, the good looking but not as usual piece of gear and then the sought after pieces of gear.

In XIV, they tried to go with an absolute freedom system which is what made pretty much everything worthless lol. Materia is somewhat correcting this and AF will definitely have a place but it seems that in the end till they finish going with the 'Required:" system that they're moving towards, anything that wasn't in demand before, won't suddenly become in demand even with potentially a lot more buyers.