Marriage is not just an individual choice. In fact, it violates the principle of individual consent. A person may consent to get married in the first place, but once they are married, they cannot just change their mind, revoke their consent, and have the marriage end when they are no longer willing to be married. They have to get permission from the state to legally get a divorce. It is not based on the will of the participants alone, and they do not get to set all of the terms of their divorce, just like they didn’t get to set the legal terms of their marriage.
My posts rarely have this many downvotes, but when they do its a post related to nonmonogamy.