My theory with situations like this is that RMTs are intentionally trying to kill the market for legit crafters, hindering their ability to make gil and increasing demand for RMT gil.

This is why you see lots of farm items in mass quantity listed for 1 gil on the MB (when any rational person would obviously just npc them for 1 gil if that is all they were worth). I suspect this is also why they took your expensive items and sold them cheaply on the MB - to crash the prices.