<p>In my opinion is because a mix of factors:</p><ul><li>War in open PvP worlds: The Big ones normaly normally decrease the price of the tcs</li><li>Transfer: the fact that you can transfer character with items to non PvP worlds from open PvP, but not vice-verse.</li><li>Resellers: most times there are players beyond the price of the tcs, playing with the market to earn money</li></ul>