Well, because the Left Can't Meme, when cuck/cuckold began to be leveled at them along with attendant jokes, they tried to "reclaim" it. First it was "don't shame people for sexual practices" then they tried (and I even saw this on CNN, I swear) to "normalize" cuckoldry, in a sort of way. But it won't stick: nobody thinks having another man fuck your wife or g/f is normal, sane, or even safe. Nobody within the majority of people do, anyway. So it didn't work. All the webcomics, all the op-ed articles, all the tweets where people (mostly soyboys) were saying they were "Proud cucks!" etc, none of it would stick.Is the cuck slur a sexual position or a pretentious, overpriced drink?
So now it's back to being a "slur" which is as it should be but anyone with a memory longer than that of a gnat knows they tried to hold up Cuck like some kind of badge of honor, and it just didn't work.