Perhaps its because the academic environment has become pretty hostile to the average male?
We still had quite a few male teachers in the early 80s but the new teachers coming in were a whole different breed and the males were all metromales.
Most of the old school male teachers had businesses aside from teaching. One owned a construction company, another owned a string of bars. Our vice principal worked on the farm with us during the summers.
Bingo.
Why enter a profession in which you are for all practical purposes expected to leave your figurative manhood at the door?