Everyone gets to participate in it. PvP doesn’t just happen at 60. Also “60-70% of the player base not getting to level 60 in 3 months” is only possible if you count the people who quit the game on the way.
Would also like to bring up how overpowered level 39-40s twinking is without BGs. You get to farm STV and Arathi and Tanaris and such while being worth 0 honor to level 60s. Yes rank caps at 6 or 7, but that doesn’t matter in a world where you are gaining honor and they are not.