“…why cant you make your hand go one way and your foot the other way without difficulty….”
Ok, sorry, I’m very literal minded and if you say, try to make a 6, I’ll try to accomplish that. Now, if you had said, move your right foot clockwise and your right hand counterclockwise, I would have said, Correct, you can’t do that without lots of practice, as Health stated.
You could do it with your right foot/left hand, though, for the same reason that when you walk you can’t swing your right hand forward when your right foot goes forward (without looking like a robot). Right foot, left hand. Hashem made us that our legs and feet work in concert with the opposite arm and hand. There is probably a lesson in there about the lower limbs, ie the body, working opposite to the upper limbs, ie the neshama, to teach us to use our neshama to counter the desires of our body. But maybe not.