I can explain it.

There is something in it for the wife. The world is a bit more "House of Cards" than some people assume. Aside from the French and a few others, western cultures seem almost uniquely dishonest about the tacit assumption that successful men will have mistresses. This isn't a new thing. Warren Buffett was essentially married to two women most of his life and no one cared.

Many wives highly value the accrued status of being formally married to a high-status person. You can take half the money but the social status doesn't follow. No one cares about a billionaire divorcee with no status beyond a bank account.