That would kind of mess up the economy a bit to trading in demonic gear, and if they did it to that gear they would have to do it to the other types. There's a reason why people buy the set off someone instead of buying the tokens and making it themselves... The same reason why people say stuff like "WTT MY AA DRAG SET+200 EC FOR UR HA DRAG SET".
200 ec or something may not seem much, but that's in one trade, consider all the trades that have been made with gear sets and the amount of ec's passed from those trades.