Please take this only as an opinion:
There seem to me to be a bunch of factors contributing to people not playing:
Fewer levelers leveling, which means less of them Qing.
Less people Q because Qs are long, which makes people not Q.
When people do play, most of the time it feels like one side gets crushed.
Horde seem pretty dominant, but that might just be my impression right now. Any faction having dominance will drive down participation on the other faction.
I don't how guilds are doing currently, but the last time I tried looking into them they seemed a bit less than friendly so I ended up staying solo, obviously if you don't have awesome people you want to play with you'll play less.