Still very busy on PS4. Activision is changing their model a bit -- they're relying more on DLC for revenue (see BLOPS II numbers) then they did with MW3 and earlier. Dropping the game's price and pushing DLC makes a lot of sense in that context.
They'll kill off their next game's player population if people start noticing that Call of Duty isn't holding its price as long. No reason to preorder/pay full price if you can wait a month and get the game closer to half off.
When people log on to their servers and the player population is lower than Ghosts' numbers (which were already abysmally low at times, I think we may see the death of a dead franchise.