Maybe he's just too one-dimensional, and too dumb (football IQ wise) to ever be a consistent threat. There will be games where what he does work for him, and he'd look good, but those games get more and more rare once teams begin to suss him out and figure out a way to stop him, and he's just not able to adjust. Now, you can say why can't his coaches figure this out for him then, and tell him what changes he can make to be more effective? Well, maybe he's too thick to apply it, or too far up his own arse to follow instructions.