Perhaps a curse from an ancient artifact. If he unknowingly disturbs an ancient tomb or touches a cursed object, it could bring about this transformation. This is a common trope in adventure - themed fictional stories, where characters face the consequences of meddling with the unknown and the supernatural.
One possible reason could be a magical curse. In many fictional tales, a spell might be cast on the husband, perhaps by an angry witch or wizard, which changes his gender. For example, in some fantasy stories, if the husband unknowingly offends a magical being while trespassing in a forbidden forest, this could be the result.
One reason could be a curse. Maybe she offended a powerful witch or magician, and as a punishment, she was turned into a mannequin. Another reason might be a deal with the devil - like figure. She made a Faustian bargain and the price was her transformation.
One possible reason could be a magical or supernatural curse. Maybe he offended a powerful witch or wizard who cast a spell on him. Another reason could be some sort of scientific experiment gone wrong. For example, if he was part of a secret experiment involving hormones or genetic manipulation, and things didn't go as planned.
She could be cheating because of unfulfilled emotional needs. If she has been trying to communicate with her husband about certain issues like family planning or career changes but he doesn't listen, she might look for someone who will. Also, sometimes a woman might cheat because she has lost the physical attraction to her husband. Maybe he has let himself go in terms of fitness or hygiene, and she is drawn to someone who takes better care of themselves.
In a fictional story, it could be due to cultural norms. If the fictional society has a patriarchal system where men are seen as superior, a man might feel entitled to control a woman. He could use traditional values as an excuse to limit her freedom. Also, if the man has some sort of secret over the woman, like he knows about a crime she committed in the past, he could blackmail her into doing his will.
One reason could be for a bet or a dare, like in many comical stories. His friends might have challenged him to do it, and his pride made him accept.
One reason could be for a costume party. The wife wants them to go as a unique couple, so she decides to turn her husband into a woman for the fun of it. It's a way to show creativity and have a good laugh together.
Another possible reason in a fictional story could be some sort of cult - like or fanatical group's practice. The girdle - wearing might be part of the group's traditional dress, and the spanking could be a form of 'cleansing' or punishment for not following the group's extreme beliefs. But again, this is just fictional speculation and not representative of normal or acceptable behavior.
In some cases, it could be due to new influences in her life. For example, if she enters a new social circle where there are bad examples or peer pressure. Maybe she starts hanging out with people who have loose morals and gets influenced by them. Also, personal insecurities can play a role. If she has low self - esteem, she might use sexual attention from others as a way to feel better about herself.
One possible reason could be a magic spell. Maybe a wizard or a witch cast a spell on the boy for some reason, like revenge or as part of a test.