Makes sense from a bounded rationality point of view. We want to be as selfish as possible while escaping punishment and social ostracism; this requires modelin

Makes sense from a bounded rationality point of view. We want to be as selfish as possible while escaping punishment and social ostracism; this requires modeling whether others will learn of selfishness, what the punishment will be, what the payoff will be, and so on. This is not necessarily quick or easy, so given the asymmetry in payoffs, it is reasonable to default to cooperation unless the additional thinking indicates that this is a safe time to defect. (Or to put it another way: is it more reproductively fit to occasionally lie? Absolutely. But if you're going to lie, you need to be careful about it. So if someone surprises you with a sudden demand or question and expects an instant response, the safest answer on average will be the truth.)