It's dropping because Bitcoin is dropping basically, the price of BTS relative to Bitcoin has been impressively stable for over two months now, hovering around 0.0005 ever since the burst of the initial bubble.
While I hope it's not really the case, Bitcoin seems to be going the way of Litecoin... A slow and steady fall as its limitations are becoming more apparent, mining is running into problems and the constant sell pressure from miners and merchants both put continous downward pressure on the price.