One possible aspect could be a desire for power reversal. In a relationship, it might be a way for the wife to experience a different power dynamic. It could also be related to exploring new forms of sexual pleasure that involve role - playing and breaking gender - based sexual norms.
There could be several psychological factors. For the wife, it might be about exploring her own sexuality more freely and taking on a more dominant role, which she may not get to do in other aspects of the relationship or life. For the husband, it could be related to a sense of adventure and exploring his submissive side, which can be an interesting psychological exploration within the safety of the relationship. However, this is all very individual and depends on the couple's unique relationship and their personal psychological make - up.
Well, it might be part of sexual exploration within the relationship. Some couples like to step out of the traditional sexual boundaries to discover new sensations and experiences. Psychologically, for the wife, it could be a way to assert her sexual desires more assertively. And for the husband, it could be a form of trust - building as he allows himself to be in a vulnerable position. But it's important to note that this is not a common or widely - understood psychological concept, and it should only happen within the context of a consensual and healthy relationship.