My theory on this is that in the 50sish when men really started to head into the office all day and the work done became more and more office work and less work

My theory on this is that in the 50sish when men really started to head into the office all day and the work done became more and more office work and less work you bring your son into (eg farm or craft works), boys learned how to be men, not from seeing their fathers, but by seeing their mothers and basically learning to be a man by not being a woman.