I read a post by a Christian sex therapist who noted that there was tons of literature out there advising wives on how to be sexy for their husbands, including being physically attractive, but that there was hardly any similar advice out there for the men. The burden of responsibility for keeping sex alive in the marriage was on the women and it was mostly to do with physical attractiveness and availability.
Also, have you noticed that most marriage books lay the responsibility on women to keep the marriage healthy and permanent? Yes, men are challenged to step up, but it seems to mostly consist of being more manly, more assertive, more macho, more masculine, more authoritative, more leader, more head of the household... all in an effort to keep the woman in line.
Sure, I sometimes wonder if I'm wrong.
BUT... I can assure you that this was my entire marital education when I entered into it so many years ago.
And I don't think things have changed that much.