A lot of marriages are purely for superficial image. Many people also fall out of love but stay together legally for various reasons.

Many ultra high net worth people are married purely for financial reasons. The wife gets whatever she wants but now they don't need to worry about losing control of their company, etc.

This is to say nothing of the biological differences either. Menopause hits some women extremely hard and libido is completely gone. Rather than divorce or mutually suffer, they open up the marriage.