Several reasons:
1. Nintendos Wii U was a letdown in the eyes of many gamers, and the game droughts only worsened on that.
2. The gargantuan gaffe of Microsoft that is the Xbox ONE reveal at E3 2013 and subsequent milking from SONY at their presentation
3. The console's GPU power. Not so much a marketing point and more one hammered down from their fanbase - and when Xbox ONE titles had lower resolution in games due to this, they milked it to death over the internet. Which brings us to...
4. Very strong and vocal Fanbase. It helps that the Xbox brand is not as well seen in europe and basically dead in japan.
5. It's pricetag at release, being much cheaper than the Xbox ONE and not too much more expensive than a Wii U
Microsoft has by now however mostly recovered from it's gaffe and token the price point out of this equation into one of their selling points, and the Wii U also seems to be slowly recovering from it's abysmal start (but by far not enough to sell really well), so I think the future will be more balanced between the consoles as it is now.







