If you want to hear some silly explanations of crying (weeping), go here.
One theory is that crying may have evolved as a kind of signal — a signal that was valuable because it could only be picked up by those closest to us who could actually see our tears. Tears let our intimates in — people within a couple of feet of us, who would be more likely to help.
“You can imagine there’d be a selection pressure to develop a signaling system that wouldn’t let predators in on the fact that you’re vulnerable,” says Randy Cornelius, a psychologist at Vassar College.
College is often a waste of money. Any human can see when another is crying, close or otherwise, and whether they decide to help is a separate issue. I am not sure whether most animals notice, though domestic animals readily pick up on anxiety.
It strikes me that the most likely cause/reason for the evolution of crying is that humans have complex emotions. Crying is an outlet for us.
By contrast: If you bug a bear in his den and he tears you to pieces, he is not trying to get saved afterward at the local tabernacle, because he done murder.
Nor is the stallion who would like to add a filly foal to his herd plagued by issues around morality.
Nor is the dumpster rat bothered by the possibility that he is disliked because he is, basically, dislikable.
Emotions, yes. Complex, no. Crying would serve no purpose for them.
Darwinism requires that stupid, materialist explanations based on survival be preferred to obvious ones that start with the reality of the human mind and human cognition, so far as I can see.