More and more cross-dressers are "coming out of the closet" and if they're lucky, their wives will accept the way they are because most of the husbands have little if any interest in having a sex change, and they simply tell their wives that their little hobby helps them wind down and relax, and will always be their little secret.
If the situation remains as described above, then it's very harmless and the marriage is unlikely to be threatened, but a small percentage of men end up creating a female alter-ego, and want to go out in public and enjoy the reaction they get out from people, and even enjoy being referred to as women, and very few wives will be able to cope with this.
They might be able to live with their husbands appearing on stage in drag, but the idea of their husbands being recognized in the local supermarket whilst dressed as a woman would be too much - and understandably so.