I think because part of the allure, at least for me, is the pain.
There is enormous pain in strife with my spouse.
To start by being honest and sharing my fantasies was incredibly painful.
"I want you to piss on me" close to the hardest thing I've ever said. The relief of being honest was better than the orgasm while she obliged.
Then was telling her about watching her with another man.
Then him cumming in her.
Then her getting pregnant by him.
Then her with a black man.
Then getting her a massive dildo and the pain when she swore she wouldn't use it.
The rock hard cock all day at work after she texted a video of her using it moaning "that big dick feels so good" as she came.
The list goes on. But to every wonderful orgasm, massive pain in indulging the fantasy and the guilt in the ones that I haven't shared yet.
The more mental anguish the harder I cum.
Doesn't take the brain long to tie the two.
I'd rather swallow a bullet than actually get cucked as part of our sex life. But if I did, I can see exactly where it would go and how I would end up immasculated to a point of losing all "normal" sexual drive.
My $.02 cents is that if you don't want an imasculated husband, this isn't the place for you. It's like wanting an ice cold fire.