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)...
Sure, why not? An X1 FPS comes out, US eats it up, a JRPG (not been a big hit since PS2 days) comes out for the PS4, isn't a stellar success. Nothing about this is unexpected. Just people getting picky over small numbers.