My son’s marriage ended in divorce after 4 months when his “wife” had an affair, dumped his stuff on the curb, changed the locks and moved her boyfriend in all before any divorce was final. I was troubled by this and spent some time discussing the situation with an old priest who was a close friend and formerly served on the diocese marriage tribunal. His advice was that an annulment in such an extreme case would likely be readily granted almost by filling out the paperwork.
Her post-marital actions indicated a mindset that almost certainly existed prior to the wedding, i.e., that she did not intend a lifetime commitment.
The idea of null marriages seems very reasonable to me. I don't know why so many people have such difficulty with it.