#4. Shinsuke Nakamura already won it while Cesaro was never an option
Shinsuke Nakamura has had multiple title reigns with the United States Championship and over a month ago, a long Intercontinental Championship reign of his ended. The sad reality is that he never gained any momentum as a Champion and was always treated as an afterthought - even with Sami Zayn as his manager.
Since it was a 3-on-1 match for the title, the idea is that the person who pins the Champion ends up as the titleholder. Right after hitting the suplex into a Helluva Kick, both Cesaro and Nakamura rolled out, letting Zayn get the pin.
In reality, it was an obvious decision to go with. WWE has established that they don't see much in Cesaro outside being a tag team wrestler, while there isn't much incentive putting the title on Nakamura.
Sami Zayn was the best choice to go with and given that he hasn't been wrestling for quite a few months now, it adds another element to the story.