I find this interesting too and I've considered why this might be. I think I may have figured it out.
I think there is perpetual dissatisfaction with any term, no matter what it is, among the black community because of deep insecurities within that community. You're probably aware that traditionally there has been a preference within the black community for straighter hair in children, talking about "the good hair" etc. There's a lot of hair straightener used... there's certainly insecurity among black women about how common and popular it is among black men to date white women, and to prefer lighter skinned black women.
There was a whole movie on this I watched recently, it came out last year I think, it was a documentary called "
Dark Girls"
There's also the fact that other racial groups throughout history have always had a particular problem with their racial group, and that even within the US they've faced racism from whites, Jews, Arabs, Hispanics, Asians, etc. All of these groups have their own issues with one another, but the highest level of disdain and
"my daughter's dating WHO?" has always been reserved for blacks, by all other groups (to my knowledge.)
There's insecurity about the associations people have with blacks and crime, etc. I think it's hard to look at the condition of black communities around the country and around the world, and to feel pride as a black person. I think this just piles on more insecurity. Of course there's insecurity about the history of slavery and segregation and all that too.
So when there's that much insecurity and a belief that everyone else dislikes you, I think no matter what term is used and no matter how carefully chosen it is to try to avoid offense, eventually it is associated with those negative stereotypes and negative feelings, and it gets "toxified" like all the previous ones did, and has to be changed out again.
Btw I'm merely theorizing what might explain what you noticed as a "oh that's a fascinating cultural thing" type of perspective, certainly not arguing that any of those stereotypes and associations are right, they are just merely historical facts.