of course a lot of it is practice and feel for the ball. Good mechanics help but you can slowly guide the ball and still have command ( not recommended - you want to use a full strong motion and still locate).
i would guess stride direction, balance and control of the lead side and head can help, but I'm not sure.
i especially ask the experts like Kyle. I'm not talking pitchers that are totally off but good pitchers: have there been studies what mechanical trait do elite control pitchers have over pitchers with mediocre control? Can control be quantified mechanically?
and what can a hard throwing pitcher that already has ok mechanics but mediocre control do to improve control without losing power? Of course a lot of practice is an answer but there are pro pitchers that throw upper 90s but never get good control ( as a reliever they still can be useful if it is not too bad). I guess those pitchers have practiced a plot, why did their control not get better?
or is control beyond solid mechanics and training just talent?