Rain, why can't girls go back to their families?

There is no such thing. Rain and solar terms have the custom of returning to one's mother's family.

(of a person) return to one's place of origin or unit.

The custom of returning to one's mother's family during the rainy festival in western Sichuan. On the day of the Rain Festival, the married daughters went to visit their parents with gifts. Women with children must bring gifts, such as canned meat and chairs, to thank their parents for their kindness. Women who have been married for a long time and are not pregnant should also bring gifts back to their parents' homes. Her mother will sew a pair of red trousers for her and wear them next to her body to show good luck and pray for a child next year.

There is a folk tradition that married daughters should bring gifts to visit their parents during the rainy season. Women who have given birth to children need to bring several cans of meat (stewed pig's feet, snow-capped mountains, soybeans and kelp in casserole, and then sealed the cans with red paper and red rope), chairs and other gifts to thank their parents for their parenting. For women who are not pregnant for a long time, their mother will sew a pair of red trousers for them to wear next to their bodies. It is said that this will help them get pregnant as soon as possible.

In addition, on rainy days, the son-in-law is not allowed to be idle, and she has to send a festival to her parents-in-law. Festival gifts are usually two rattan chairs wrapped in a 4-meter-long red ribbon, which is called "Shoushou", meaning to wish parents-in-law a long life. Another typical holiday gift is canned meat for men, which is for parents-in-law. This is to express gratitude and respect to the parents-in-law who have worked so hard to raise their daughters. If it is wedding date, the newly-married son-in-law, her parents-in-law will also give her an umbrella in return, which is intended to bless her son-in-law to go out smoothly and help him keep out the wind and rain, and also to wish her a safe life.