The whole BG balance thing was put in during the L40s cap back in Aeria. Not too sure if it can be changed, without source, @Vivi to confirm.
I wish we could change the game to where if you reg for a BG, it forces you to go into BG, regardless of where you are. None of this "confirming to join" nonsense. Don't know if it's people trolling, or AFK, or mis-clicking and accidentally cancelling their invite.