One reason for a divorce dismissal is known as "want of prosecution" based on failure to serve the respondent. After a spouse files a divorce case, she has a certain amount of time to serve the divorce papers on her spouse. That amount of time varies from one state to another. If she does not serve divorce papers on her spouse, the court will eventually dismiss the divorce case.
In some states, a court can dismiss a divorce case even after the respondent has been served if the case becomes inactive. Twice a year in Alaska, for instance, the court clerk must review the active cases to identify files where proceedings have not been taken. The clerk notifies the parties in inactive cases that their case will be dismissed unless they contact the court within 30 days to explain why the case should not be dismissed. If no one responds to the clerk's notice, the clerk must dismiss the case.
Sometimes the spouse who filed for divorce will decide to dismiss the case. This sometimes happens when a couple reconciles. It also can happen if the filing spouse reconsiders the timing of the case and decides to dismiss it now and refile it later. For example, she might plan to refile when her children reach a certain age, when her husband graduates from medical school or when the couple earns enough to support two households.
A court could issue a divorce dismissal if, during the divorce proceeding, it comes to light that the couple had never been legally married. A divorce proceeding dissolves a marriage. If a couple was never legally married, they have no marriage to dissolve. If the judge determines that one of the spouses was already married at the time of the marriage, one spouse was under age or the marriage falls into another category that could nullify the marriage, the judge will dismiss the case so it can be refiled as an annulment proceeding, not a divorce proceeding.