Because life is full of uncertainties, randomness and unfairness. Even the most successful ones are not inmune to this. Steve Jobs was fired from his own company and died of pancreatic cancer at 55.
Let me guess the conclusion: the natural situation is for one guy to be the biological father and some other guy to pay for the care as shown by the resourcefuls himba but in civilized countries this is not possible because of the damn patriarchy?