The pragmatist in me says it is a direct result of the high stress of the farming lifestyle (I say lifestyle because it is more than just an occupation for a lot of people). Stress is caused by many factors weather, working in a highly regulated market, low income for the small traditional farmer, worrying about loosing your farm to the banks / tax-man, little respect from those you feed, etc.... and then pile on top of all that seeing your children reject that life and moving away, it would be more than a lot of people could bear, I would think.

Proverbs 22:6
Train up a child in the way he should go: and when he is old, he will not depart from it.