Nice in theory, but it would turn the simple question "Is Bob married" into a complicated examination of the contracts to which Bob was subject, and could easily lead to a situation in which some people would regard Bob as married while other people did not. A total mess. To be sure, such situations can also arise in states with Common Law marriage, but having everyone draft up their own "marriage contracts" would make things even worse.
A contract is a contract. It wouldn’t matter what other people “saw”. If they want to sue each other over it, that’s fine with me. Stupid people should be separated from their money, even if that means getting lawyers involved.