This rarely-used ground for divorce illustrates why "no fault" divorces are heavily favored by modern practitioners. Judges are wary to turn the courtroom into a "Jerry Springer"-type environment. A divorce is an immensely personal transition. Given the social stigma of the word "impotency", there is a high risk that any divorce action citing impotency as its grounds will make it more difficult to come to any agreements with the allegedly impotent individual, and the courtroom could likely become a forum for uncomfortably personal critiques.
In a "no fault" divorce, the judge need only be convinced that there has been an "irretrievable breakdown" in the marriage with no chance of reconciliation. In practical terms, all that means is that one spouse needs to be able to tell the judge just that.
By contrast, in order to obtain a divorce citing impotency, the court needs to be satisfied that your spouse is incapable of having sexual intercourse. This can obviously be embarrassing to one or both spouses. Other than the added embarrassment, and the increased likelihood that the divorce proceedings will become more difficult to resolve, there is nothing else to gain. The division of property, child support, alimony, and visitation will not be affected by impotency. As such, very few practitioners choose to plead impotency when filing a complaint for divorce.