WoW PvP participation dropped drastically from Legion S1 to Legion S2 despite S2 being 4/3s of the duration of S1.
50% drop in alliance participation (the biggest drop in WoW history)
30% drop in horde participation (the second biggest drop in WoW history)
Feel free to lol a little:
https://us.battle.net/forums/en/wow/1011696/
This one is actually my favorite:
https://us.battle.net/forums/en/wow/topic/20754075338