I don't know myself, but I wonder if the answer lies somewhere in the Shift Happens book.
I haven’t finished it yet but what I’ve read so far implies that a few things converged. The first electric carriage returns added a motor on the right-hand side that pulled the return lever mechanism. The bottoms to operate it were near the motor. The first mechanical typewriters with integrated electric returns also put the button on the right. A bit later, for reasons I haven’t gotten to, early postwar teletype innovations added line feed and carriage return buttons, also to the right. And by about 100 from where I’m at, all the first electric typewriters are putting the CR buttons… on the right.