It's pretty simple really and I understand some people just refuse to accept it but really it's just that the X1 is simply not a desirable console. Especially when compared to the PS4.
People seem to think that just by virtue of being an Xbox, it should be selling, but this isn't the case at all (see Wii U). It also needs to be desirable and honestly, outside NA there's zero reason why one would pick an X1 over a PS4. And in NA, the PS4 is overall more appealing hence it's doing better.
Let's look at it this way, the X1 biggest game is a remaster of games that can be played on 360, everyone that wanted to play them played them last gen. Something like Last of Us works because due to the 360's domination last gen, millions of people (many of whom are no shifting to PS) missed out on it. Halo though? Yea, everyone who wanted it played it and while it will provide a boost I feel it'll be very much like TF in that everyone who wanted an X1 for it mostly already buy it. And before anyone comes in and says "well I'm buying an X1 for it", yea, that doesn't mean much as it's just anectodal, I'm speaking about overall.
And if you're thought process is then "the PS4 doesn't have any big exclusives", my answer is simply, the PS4 doens't currently need exclusives to sell. What it does have (TLOU, DC, and LBP3) will more than enough as it's selling primarily based on third party titles, most of which are better on the console anyways.
