In such stories, one possible motive could be revenge. Maybe the wife feels wronged by her husband in some way and wants to publicly embarrass him. Another could be a lack of self - control. She might be easily influenced by someone else and give in to temptation without thinking about the consequences.
In the context of these stories, there could be multiple motives. Firstly, a sense of self - entitlement. She might feel that she has the right to do whatever she wants regardless of her marital status. Secondly, a desire for power. By publicly cheating, she might be trying to assert her dominance over her husband or show that she can break the rules. And thirdly, it could be a result of her own insecurities. Maybe she feels unloved or unappreciated in her marriage, so she seeks validation from someone else in a very wrong way.