Xbox continues to do well in the US because Microsoft did an excellent job of making people feel invested in their ecosystem.
In much the same way that players often resist leaving an MMO because they "lose" all the gold and rewards from their efforts, creating an environment with things like gamerpoints, achievements, and friend networks keeps people from easily switching consoles the way they did in the past.
Many people have little interest in deep single-player games, as well, which largely negates the exclusive advantage. Something like The Last of Us wouldn't even be on their radar.
Microsoft has catered to this demographic from the beginning and they've managed to keep many of them despite their missteps this gen.
The reverse is also true. Many gamers couldn't care less about multiplayer and prefer singleplayer experiences like GoW or BotW over SoT. For those, Xbox probably isn't the right console right now.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454