The price. Check the fares on both AS and VX sites before booking.

VX is setup like a Codeshare for reservations for right now, certain fare classes aren't available outside VX. Seems to be sale fares only, same itinerary on a LAX-FLL trip was about $100 more on AS.

Both AS and VX use Sabre but slightly different flavors. System rules need to be loaded and tested. Getting two databases to talk to each other that never did before at this level doesn't happen overnight.