I don't know the reason for such stories. It might be part of some dark and unethical fictional genre or just a random, offensive idea someone came up with. Such themes are best avoided as they have no positive value.
This is clearly unethical. A relationship between a husband and a wife should be built on mutual understanding, trust and respect. Using such offensive language to describe a spouse is unacceptable. It can cause great harm to the relationship and the person being described, and it also sets a bad example for others in terms of relationship values.
Rather than focusing on such offensive concepts, we could look at stories about loving, supportive and equal partnerships between spouses. For example, stories where couples support each other's dreams and grow together.
Well, some of the themes could be the exploration of forbidden desires, the challenge of societal norms, and the internal conflict of the characters involved.