Why? It goes down even on days the market is down modestly, VXX needs triple digit down days like today to go up and there are not many triple digit down days to get the trend in VXX to go up.
Example on Nov. 12th when the market was near 11k on DJIA it was $48+ today the market is back to 11k on DJIA and its only at $44.92 , so its lost +$3/shr while the market has not gained at all in the same time frame.
It falls alot more on up days than it does on big down days and on just small down days it falls again.
So basically you win 2 out of 3 times with VXX on the sellside.