Why is it that my drumstick in my dominant hand always hits the same spot yet the drumstick in my non-dominant rarely does?
Mainly due to the dominant hand/wrist/arm having years of practice being pretty accurate , whereas the non-dominant one/s have been lazy!
If you had used both equally in all sorts of tasks - throwing a ball, punching, picking up, prodding, swiping, the list goes on, then they'd be about equal, and you'd be fairly ambidextrous. Which is a good thing for a drummer.
Even with matched grip, that non-dominant limb needs to catch up on the years of practice its partner has over it. Try to favour it more - after all, the dominant one can pretty well cope.