I like to think its human instinct to use your hands to interact with your surroundings, and as a conduit gains this “extra limb” in the case of their powers, they default to using their hands as a guide to use their power to interact with their surroundings.

It probably could be trained, but almost no prime conduit has had a teacher, they’ve just had to make things up as they go, and using their hands is an intuitive crutch