This might be different with the people everyone else plays with, but I find about a good 80%-90% of the play population will only step foot in any kind of PvP content because of good series rewards. (Myself included). The mode is absolutely an afterthought, its horribly unbalanced in just about every way in all aspects of PvP (CC's, health, damage modifiers, defense modifiers, ability damage) The maps to play are all either just made long ago and the design was an afterthought, or they're new like Crystaline and suck anyway for a push the cart type map. Bugs and glitches that get reported for PvP take months to fix, and there's still literally no matchmaking system. You can't go in with a party, so yes, of course it's an afterthought.

If there weren't some fancy rewards at the "very end" of the series, I wouldn't be surprised if only about less than 10% of the entire population stuck around to "continuously play" PvP.