Changes in Support Systems
On my support groups I have noticed that a lot of the spouses of mental patients end up being mental patients, because they break down under the stress of living with mental illness in the house.
A generation ago, the family would be in the same town, sometimes the same block, as most of the extended family and friends from grade school.
Even if the problem was a family secret (as mental illness might have been) the spouse and children would be supported, both emotionally and financially, by family nearby.
If children were being left in the care of an unstable mother, her mother or sister would check up on her frequently and often spend the day with her so the children wouldn't be neglected or abused.
There were a lot more ways for a man to make a living that could be worked around some mental illness. The patterns of activity in crop farming tend to mimic the patterns of activity of some forms of bipolar disorder.
Hybernating in the winter, like many with an annual bipolar cycle do, may be an adaptive behavior that would have worked in an agricultural society. Matched with the long hours of hard labor that would occur during planting season (spring mania) and harvest (fall mania) which would also be acceptable behavior.