Commenter Johnny Redux nails the answer to this post’s title with an ugly truth few men, let alone women, would be willing to confront head on, obliquely, or deniably:
A sexless marriage, in many (if not most) cases, is the result of a man marrying a woman his own age, and after time losing all sexual interest in her as she quickly morphs into an old woman before his eyes, much quicker than he is aging.
Men are maximally attracted to young women.
Men age more slowly than do women. (At least going by outward appearance.)
Men’s sexual worth