Why don't I cry more?

I asked this question and I realized that a lot more adults cry more often that I thought. I almost never cry, and when I do it’s as privately as possible.
In the example I gave in that other question, where my daughter was moving to Washington with my 4 year old grandson, I waited to cry until that night, when the kids were in bed.
Why don’t I cry more? Is it because I can only remember my father crying once, same with my mother? Or is it because I feel helpless when I cry, and I don’t like feeling helpless?