A lot of students want to work then, so it is really rare for us to have an open spot at that time of day.

Part of the answer is probably that not all the negative consequences would have shown up at the time the mechanism was evolving. Obesity, for example, is rare in a state of nature.

Considering how much time the role of product owner takes, however, it is relatively rare to find a product owner that would have the capacity to take on development work as well.