I don’t have any interest in making any sort of contract with the state. A marriage contract requires the state to be the enforcer. Unless you’re talking about an unwritten contract between a man and his partner. That’s fine but not marriage in the traditional sense.

You’re right that it is not guaranteed to fail but the odds are a coin toss that your marriage will fail. And that doesn’t account for the number of marriages that are miserable but stay together for the kids or because divorce is expensive. I know a decent amount of people that have been separated for many years but still legally married. Even more that are trapped in a loveless marriage where cheating is likely happening or inevitably going to happen.