1. Traditional ideas: Some traditional ideas hold that the woman's parents should not be too active at the wedding, and the man should propose or arrange time for his parents to meet. So if the man doesn't have a formal invitation, the woman's parents may choose not to go to the man's house.
2. Family status: In some cultures, the woman's status in the family is relatively low, and the man's family may think that the woman's parents are not important, so they are not invited to the wedding.
3. Time and economic reasons: Some women's families may not be able to attend the wedding due to time and economic reasons, such as work and inconvenient transportation.
4. Family relationship: Some women's families may be unwilling to attend the wedding because they are not harmonious with the man's family.
It should be noted that these reasons are not applicable to all situations, and the specific situation needs to be analyzed according to the specific situation. If the woman's parents don't attend the wedding, they can explain the reasons to their relatives and friends in other ways.