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.