I think the transition for console gamers going from 24 players to 64 along with the upped graphical quality has been the key factors. It seems many have warmed to the sheer scale of the game along with the quality. Call of Duty is such a last gen game now and the contrast between both FPS games is massive. Even when it was was released on PC; Ghosts didn't look much different from MW2 and the 6v6 format is just embarrassing particularly on the larger maps.
Players currently online:
PC
88,394
PS3
91,507
XBOX360
86,795
XBOXONE
56,145
PS4
76,093
(source; bf4stats.com)
PC has been very consistent along with the old gen consoles but 76k for the PS4 is staggering and it's only a matter of time until this eclipses COD. How many does Ghosts get on the PS4 usually? On PC, Ghosts averages probably 10k and peaks around 30k.