"Why do you cry?"
"You mean people? I don't know. We just cry. You know. When it hurts."
-Terminator & John Connor, Terminator 2: Judgment Day

Crying relieves tension and is a means of communication. The only way for infants to express frustration, pain, fear, or need is to cry. Adults may use crying to bond with other humans. Expressing sadness can prompt comfort and support from peers. Different languages can provide barriers to spoken communication, but emotions are universal.
-Scienceonline

We don't often see characters shed tears in SW, in fact, I can only recall 4 instances, most of them involving Anakin. All six films contain very emotional elements; there are plenty of reasons, both happy and sad, for our friends in the GFFA to cry: the relief and joy of the destruction of the Empire being celebrated with old and new friends, the death of loved ones, loved ones in pain or danger, loss of home or leaving home, and physical pain.

I suppose GL didn't want his main characters to cry too much as it could slow down the action, distract from their duties or be perceived as a distraction from their courageous demeanors. The only character (besides Luke in ROTJ) that GL made it a point for us to see cry is Anakin. He cried in ATOC when he told Padme about his experiences at the Tusken camp when Shmi died; he cried in ROTS when he was worried that Palps might be killed during his arrest (and the dark side knowledge that Palps "promised" him would be lost forever), and he cried on the bridge at Mustafar when he thought about the atrocities he'd committed. He felt things deeply and his emotions affected him.

We see Luke cry only once, at his father's funeral pyre. Luke must have been feeling conflicting emotions: sadness that he'd never get to know Anakin, relief that his father returned to the Light, and happiness that his instincts about his dad were correct.

These two men, father and son, were not afraid to cry. They needed to express their emotions. That seems un-Jedi-like, but maybe that's the point. Maybe that aspect of Luke and Anakin presented unique struggles on their paths to becoming Jedi, which they each met in their own unique ways. Maybe this represents our struggles on our own paths, which we must meet in our own unique ways.