If I wire millions on exchanges (the thing that should happen in order for BTC to go in a sustainable uptrend again... which doesn't look like it's happening by looking at the decreasing bid sum) nobody knows what I want to do with them in advance. Once I have them on the exchange, I can short all I want. And if I am an hypothetical entity that has the mission to kill confidence in bitcoin, I don't care about losing them all. It's that simple.