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....
Researched this subject some time ago, and came up with the conclusion you can blame Igor. His machine only had one collective, placed between the two seats, he preferred flying from the left seat so students he was teaching flew from the right. When they went to an operational squadron guess which seat they preferred? Some veterans here will have experience with the single collective between the seats on the Sycamore. Know why PIC sits in the left on a FW? Early days of airline flying in Europe it was all VFR of course, and a decree was issued that aircraft would fly to the right of the navigational feature they were following (railway, road), left seat thus enhanced map reading ability. I could find no better answers.