Because sadly there really isn't much to do in the open world. Unless you're farming FATEs, gathering, doing the tribe dailies in that general location, a quest, or getting TT cards, there's nothing to really do in those areas. There's nothing social in nature. Most people I see are either in one of the city-state/Gold Saucer, in residential areas, or are currently running instanced content. There's a reason why mega-servers became a thing in GW2 for the various areas, because they had similar issues with empty areas happening.
