Rotors turn a different way for the same reasons that propellers vary their rotation. It all depends where the drive is taken off the engine.
All engines rotate clockwise looking from the front. If one attaches the propeller on to the crankshaft at the front of the engine the propeller will rotate clockwise looking from the front. In the USA the propeller drive is normally taken off the back of the engine where a clutch would be in an automobile so they turn the engine around so the propeller is in front therefore the propeller goes anti clockwise looking from the front.
Helicopter drives to the gearboxes using a similar speed reduction system will cause the rotors to go different ways according to the design of the piston engine. With gas turbines you arrange it so that it goes the same way as before.
An example is the Super Frelon. French designed and built but the only one with an anti clockwise rotation because the rotor system was licence built from Sikorsky.