I think the dude just doesnt trust his own body enough. Maybe he's scared of punching himself out and losing all his stamina and getting in more danger of getting stopped, and he realizes that he's still just in the middle rounds. So he just cruises along, jabs and jabs, accumulate points and rounds. Sometimes throwing a hard shot here and there. And then when he sees it's only 6 minutes left in the fight, he pours it on and gets more aggressive. I think that's it.
If you ain´t got the balls to really win against your opponent you´re in the wrong game. Same as in the Tyson decade. If you come scared you will be punished...