Hangover from aeroplanes, throttle controls in a side by side configuration are in the middle of the aircraft hence pilot sits on the left, right hand (not being leftist!) being more precise to control the engines, the left hand can maintain flight control. Helicopters followed suit initially but very soon realised the control column/cyclic needed greater accuracy of control and the collective could be operated more agriculturally hence on the left. Second order consequence, the collective fouled ingress and egress, simple solution, move pilot to the right.
It’s a theory....