You have to look at the market itself and see what the competition is offering.
PlayStation 4 has had a string of high profile and "exclusive" releases since the turn of the year. Kingdom Hearts, MLB 17, Nioh, Persona 5, Nier Automata, Crash Bandicoot and Horizon. They're offering great bundles, great pricepoints and with the 1-2 punch of VR and Pro, they're still riding the wave from late 2016. There's a lot of attention on the machine and it's consistently getting good games releasing which you wont find on Xbox.
While they're already the platform of choice for the mass market, the continued support from developers and Sony themselves just solidifies this position.
Nintendo Switch launched to huge fanfare with one of the greatest games of all time. It's new, it's exciting and it's got a plethora of exclusive content already planned. It's essentially been sold out since release and it's stealing any real "2nd console" consumers who would have looked at an Xbox One as the companion to a PS4 purchase.
Now when you compare those two platforms to Xbox One in 2017, you basically see that Microsoft have offered nothing worthwhile on the platform that can't be played on rival platforms since what, Gears 4? In October? They released Halo Wars 2 this year and that's all I can think of. When the competition is making moves on an informed and motivated consumer and Xbox is sat with nothing to appeal to those consumers, you'll start to see numbers like the ones we're seeing right now.
