I was a bit sarcastic, but not much. Reality is that most long-term marriages experience significant decline in sex life. Why is that? I have my suspects, but I guess it would actually be a complex problem, contrary to the popular view.
Discussion
It's because people get old, if they've been married for a long time.
They're still having sex more often, than people who aren't married, who are the same age.
Seems intuitive, but is it so, really? I was researching that years ago for a study that I haven’t written yet, and there are so many variables, but marriage seems to associated with greater decline in sex life. I suspect that it’s because statistically it forces to stay together couples who otherwise wouldn’t. But serious research is scarce, mainly because people tend to lie about this big time.
Because the man stops growing and starts acting like a child that the wife has to mother, causing the wife loses attraction for the man, causing resentment
That might be one reason, of course. But this doesn’t happen in isolation. Both genders are being very immature nowadays and women are especially encouraged to avoid responsibility. It’s a strange world.