The author believes that this is not because parents are crying, but because parents are so excited that they are in tears. In other words, what comes out of the eyes is tears, not tears that come out of crying.

Parents are happy to see their son get married. Starting today, parents will give their son to another young man. Parents finally relaxed and put down the burden of education and support for more than ten years and twenty years. And in a year or two, the family will think that having a daughter-in-law will add people to import, flourish and prosper. How exciting it is for parents!

Therefore, parents were so excited that tears filled their eyes.