There’s no emotional connection.
One of the many reasons why women after 50 decide they want out of their marriage is that they no longer sense any kind of emotional connection to their spouses. They might have developed routine patterns of relating and behaving that keep both spouses apart from each other, even if, practically, they are still living together.
All they do is get up to go to work, come home, and repeat. Also, on weekends, they might have other things to take care of. Maybe their children are back home, or they have completely separate interests that they prefer to indulge in rather than spend some time together. Oftentimes, instead of turning toward each other, spouses drift apart, and this is a real crisis point in any marriage.