The answer is actually quite scientific:
The average man's shoulders are 18.25" wide, allow for an external rotation of 7 degrees for each arm, plus an additional 85 degrees for the hands gives you a width of 22" (external cab width). During the wide body craze in the 90s there was a significant increase (300%) in shoulder and upper back strain due to the un-natural stance required to accommodate the wider cabinets.