Only undisclosed blindness itself would render a marriage voidable. Using the theory of latent psychological defects in such a blunderbuss fashion flies in the face of the cardinal Jewish belief in free will. Each of us is born with a wide variety of tendencies - some towards good and some towards evil. But Judaism insists that we are not determined by those tendencies. We have the ability to overcome our innate weaknesses, as well as to squander our innate strengths.
People can, and do, change.
Perhaps he repented in his heart. What we are after 20 years of marriage, cannot prove what we were 20 years earlier. The heads of the annulment beit din offer one more ground for annulment. Therefore every marriage is voidable. In one fell swoop, they have cured the problem of Jewish divorce by doing away with Jewish marriage.