#4 Lack of faith in Rusev as champion
Let's be honest here, as much as the WWE Universe continues to be behind Rusev and his Rusev Day gimmick, WWE just doesn't share that belief. Not only is that extremely evident by how little the United States title has been featured since Rusev won the belt, but also by how uninteresting the storyline between Rusev and Nakamura was.
If nothing else, taking the title off of Rusev was a mercy kill of sorts for the misguided title run and gives the company a chance to script something better in the future. Of course, those plans might not involve Rusev after what happened at the Royal Rumble, but whatever the company ends up doing, it needs to be better than this.
In the end, Rusev as champion wasn't working. His promos weren't interesting, he didn't have the needed charisma and the storyline build around him wasn't doing him any favors either. Again, it's a mercy kill and it's hopefully a promise of better things.