natural selection. cooperation is a dominant strategy in indefinitely repeating games of the prisoners dilemma, for example. We also have to mate and care for our young for a very long time, and while it may be true that individuals can get away with not being nice about this, we have had to be largely nice about it as a whole to get to where we are.

while under the umbrella of evolution, if you really want to boil it down to an optimization procedure then at the very least you need to accurately model human emotion, which is wildly inconsistent, and our selection bias for mating. If you can do that, then you might as well go take-over the online dating market