I have wondered if it is somehow transferred over from bowed instruments, where the bow requires strength, finesse, endurance.
Not very confident of this idea though.
I think you are on to something there. With guitar the right hand just does the strumming and the left hand does all the intricacies of creating chords.
BTW, I am left-handed. In about 1964 or so some of my school mates wanted to start a band and asked me to take up the bass. I started playing lefty, but when I tried to buy a bass the options were play an upside down bass or pay bunches for a left-handed bass. I chose to learn to play right-handed.