I'll add . . . .
He's a pocket passer for a reason. He can't run for crap.
He's very good at getting rid of the ball fast; and/or can't extend passing plays, because of the aforementioned lack of running ability.
Doesn't get sacked a whole lot.
So he usually never gets into a bad situation running for a first down and the gets clobbered, or doesn't scramble around try to pass the ball.
(e.g.
RG3,
Cam,
Flacco, etc)
His lower body is not explosive; he couldn't pull a hammie, or strain a quad or calf if he wanted to.
Top fuel dragsters blow an engine every fourth race. Your mom's subcompact grocery-getter? not so much.