Because the amount of volume that was required for this drop was much lower than normal due to lack of moral around false news brigades, now that we hit 50% of the price the volume didn't match the amount of the 900 -450 drop until all the buys back in.  Its going back up, people try to compare this to April where we had MtGox go down, Lag for 4 hours (with no GoxLoop™) and the blockchain forked.  Of course its different this time, not for no reason but for those reasons.  Don't get caught up in the greed train..