With helicopters it's certainly not due to the direction of rotation of the rotor blades. After all a Puma's blades rotate the opposite way to a Sikorsky's, or other American machine.
Most pilots would be right handed and therefore would hold the cyclic in their right hand and the collective in their left hand. Having the collective in the centre of the aircraft is better. Of course the other pilot has their own collective as well, but that is ownly in machines with two pilots / dual controls.