Maybe because PS4 easily outsold One in March despite the price cuts and TF. Now that the price cuts and TF hype have died down, we are to believe X1 sales are actually increasing while PS4 falls (and it even had FFXIV this week)...
I wouldn't expect FFXIV to increase PS4 sales much but I'd certainly expect the game to help sustain sales. Take 20k off of the X1 numbers in America, increase PS4 numbers by 10k in America, add another 20k to the European numbers and I'd go with that.
The PS5 Exists.