The way I see it, if women actually are so unattractive after 30 or 25 or 35 or whatever, her husband is the most attractive guy she's going to get, EVEN IF he's a beta or not that hot. Because the single men who aren't her husband are going to be either out of her league, or the most desperate of the desperate to be into a woman her age (who has kids nonetheless) and therefore less attractive than her husband, because if they weren't, they'd have better options (younger women, women without kids, women who are single etc)

There may be a few decent looking guys who would be interested in her solely for sex, but no woman, even a complete idiot, would end her marriage for the sake of a ONS, plus any study on female infidelity show most of this stuff starts as emotional affairs and genuine "branch swinging" as in, "leaving my husband for this guy." It's men, not women, who are more likely to just have a ONS or casual fuckbuddy situation due to sexual boredom or neglect (Not saying either motivation is more noble, they're both shitty, just different.)

So, it seems to me that if you don't act like a complete dick or completely give up on life, the chances of your unattractive post-wall wife finding anyone better than you to branch-swing to are pretty much zero, right? Why on Earth is this something anyone worries about when it's also assumed that no man is going to want a woman her age who's had kids? If she's a woman around the same age as you, it's kind of a guarantee that she won't be able to do any better than you, ever, unless you gain like 300 lb and stop showering.

Who are these attractive men who have nothing better to do than steal unattractive women from their husbands?

TLDR If women aren't attractive after 30, then there logically wouldn't be anyone better than her husband who would be interested in her, especially not interested to the point of convincing her to leave the guy. Any attractive man, theoretically, wouldn't have to stoop to this level and could instead just be with single attractive women.