I suppose it needs to be said... some of these cases of men killing their families, then themselves, have the look of organized crime cases.
The Scenario: A guy gets into deep financial trouble. He owes a lot of money to a number of people, who themselves may have debts. Some people are desperate to enforce debts because the financial failure of their business would exposure their illegal business operations. They enforce debts by threatening to go after the family, as in, "We know where you live, where your daughters go to school. We'll turn your daughters into sex slaves if you don't pay up."
Faced with this, and the belief that the corrupt system cannot protect them, they are led to the only logical conclusion.