Here's a controversial theory: Uriah is just too nice of a guy. He's not bloodthirsty enough, he's not ruthless enough, he cares about his opponents too much.
Remember TUF? Hall felt genuinely SORRY for knocking the other guy out.
I don't believe in "alfa males" and shit but I do think that become the absolute BEST in such a violent sport you need to be either bloodthirsty (enjoy destroying the opponent) or completely cold-blooded (emotionless).
One could argue that Fedor was both - his face showed no emotion but he said himself that he used to look at his opponents as people who wanted to take food away from his poor family. Jones was bloodthirsty - he enjoyed hurting ppl, stomping knees, eyepoking etc. Wandy was bloodthirst incarnate. Anderson was cold-blooded. And so on.
If you're "only" skilled and athletic (which Hall obviously is) you may end up a gatekeeper (which is who Hall has become). There are many awesome fighters who just don't "smell the blood" - I think Wonderboy is a great example. He has all the tools to be champ but he's too hesitant.
There are exceptions of course - like Machida, who is neither bloodthirsty nor ruthless but he was able to go into fights with an emotionless "empty mind", which is hard to do.