In the recent month I found that the trend of VXX has deviated significantly from VIX futures. Both the September and October VIX futures have been in down trend since late July, while VXX stayed pretty much at the same level. Since VXX holdings are composed of near-term VIX futures that are in contango, I would expect VXX to be in a faster down trend due to the rolling loss. However, that is not the case. Why aren't arbitrageurs short VXX and long the futures? Am I missing something?