My take on it is that VERI is all about peer-to-peer, and most of the exchanges are centralized.  EtherDelta is decentralized.  I'm guessing the centralized exchanges don't want to support something that ultimately will make them obsolete.  With that said, I think there is one advantage to centralization, which is with respect to the fees when placing orders.  When you place an order on EtherDelta, you need to pay a fee regardless of whether the order completes.  On a centralized exchange there is no fee unless it completes.