PVP as a whole needs a big changes add PVP gear to the game that does something besides glamour, make it intressting maybe add chests or something that contains random stuff.
Frontline is the only thing that pop frequently because it's tied to the Daily roulette.
I heard Rivalwings pop at certain days because theres a discord for that.
and lastly Feast player base is so small it's basicly the same 10-15 ppl that play the mode at gold,platinum,diamond rank.

Datacenter splits pretty much ruined PVP and made it less active all across the board.