I think it depends upon the relationship that they had before cuckolding. The kink is one thing, reality another. If the relationship was very strong before, and if the wife wanted something specific out of it (like trying BBC), then there is no fundamental reason for her to leave her husband. It can be a way for a woman to try sexual experiences she missed out on before marriage, or a way to indulge yearnings that I think a lot of women have but supress. So, if the true motivation was one of these, then cuckolding can make a marriage better.
This hits it on the head. If the marriage is great and the only reason for the extramarital sex is a mutually agreed upon experience intended to expand the wife's sexual pleasure, it's a good thing. If it is being used as a way to try to "fix" something perceived to be missing or unsatisfactory in the marriage, it will most likely end in disaster.
The bigger problem is the fact that cuckolding does lower her husband to beta status on a psychological level. A lot of wannabe cuckolds don't really prepare themselves for this reality. And it is a real thing. The fact is that you are raising this other man to Alpha status over you when you ask your wife to share her most intimate parts with Him. I think a lot of women know that this will happen if they go down this road, and thus are reluctant. But it can be overcome in a strong relationship. Having a strong relationship is totally key and important! Otherwise do not tempt your wife with another man, lol!
This is mostly true depending on the reasons the husband is becoming a cuckold.
In the case of a man who has no insecurity about himself or his relationship with his wife and is doing this as an act of love to give his wife the most pleasure possible, he is not lowering himself at all. If anything he is elevating himself. He isn't giving the other man status above him, but rather making him an extension of himself sort of like having grown a second penis or another pair of hands with which to use to heighten his wife's pleasure.
On the other hand, if he is becoming a cuckold out of a need to experience his own fantasy rather than as a service to his wife, then he will experience that which he is imagining, which is most likely an expression of a male who feels himself to be "less" worthy. Here the husband is surrendering his place to another he deems superior in ability to satisfy the wife.
You are totally on target with many women being resistant to exploring their husbands desires to be cuckolded for that reason. They instinctually know that if they allow their husbands to go there, he won't be able to handle the emotional riptide and they may lose him to his own demons.
Of course, most women don't have a real desire to cuckold their husbands if they have a good sex life within their marriage anyway.
My Wife has been with other men of many races before me and has no desire to have a lover at this time. I would love to watch her with another man or woman or even join them to give her extra hands, lips, tongue, etc, but that is my fantasy to own until such time as she finds someone that she would enjoy experiencing sex with.