That's his body shape and he's not trying to maximize his physique potential by doing pec deck flyes and lateral raises as these types of movements aren't gonna help much in a fight.
when I was training it was shit tons of grappling, lots of pushups, lots of situps, and lots of sparring followed by more grappling. Weight training was almost frowned upon. When I asked what weight training I could supplement my time at the club with, they snickered and said 'lifting heavy weight isnt going to help you when youre gassed out abd cant move your arm anyway'....
I thought it was an old school mentality and the strength couldnt hurt anyway, but he was right... I always gassed quicker than some of the other guys that didn't lift and did nothing but cardio, sparring and grappling. Then again, I was a beginner and was still working on my endurance when I stopped as well.