[vikingerik]

I think this reason is dependency. Anything I'm doing where the action of one hand depends on the other has to go left-to-right. I can only finger frets with the left and then pick with the right. Can't go the other way, can't have the right hand act before the left, even if the left has the more complex task.

It's like Super Mario Bros. With a 4-way d-pad and 2 action buttons, why is the more complex 4-way on the left? Because most of the time you're holding a direction first with less requirement for precise timing, and then pressing the button at the correct instant depending on the movement. (We're talking general platformer play, not hyper precise d-pad moves for something like Super Metroid speedrunning.)

Even typing on a keyboard, I never hold a right-side shift or other modifier key, it's always left-shift then the target key.