I would chalk that up to differences in culture and how the communities of each express themselves. And there are plenty of modern themed manga that have slavery adjacent tropes, you're either ignorant or just choosing to ignore them. The slavery trope is just easier to insert into isekai and fantasy genres because that's where Japanese culture expects to find that type of slavery. In more modern settings slavery presents itself more as Yakuza loansharks, black companies, and ugly bastard porn.
Isn't that just the nature of manga and anime? Both have always had a twisted sense of reality that barely parodies a given subject. So it's not all that surprising there is only an idea of a real world topic in this type of media.
As for my point, it was only that just there are real world cultural reasons for slavery to be seen in isekai and fantasy media.
Lol. Now you're just going for abstract concepts to try and cobble up a way to justify your earlier take that you accidentally annihilated yourself by comparing it to American slavery. Now yakuza, black companies, and ugly bastard porn is on the same level in this context? Are you even lucid at this point?

Comparing American slavery (race politics) to Japanese concepts of slavery in WWII with a straight face and you actually have the gall to call me ignorant? What, now it doesn't have to be romcoms? You're being intentionally obtuse (shit, probably unintentionally) to try and strawman the argument again. Stop it.
As for my point, it was only that there are real world cultural reasons for slavery to be seen in isekai and fantasy media.
Except if that was actually your point, nobody would disagree. That sort of broad stroke makes perfect sense. Why?
Because yes, exactly, it's not that deep. It's the specificity that you used, and not only used, but used to disagree with, that reads like bullshit. Because it is. You tried to reframe what I said so many times at this point to suit your nonsense that you really need to take a step back. I think it's very clear that you have some preconceived notions of what you think the average Japanese thinks of slavery.
Like gee, I wonder why it's "easier" to insert slavery (in the way we understand it, not your abstract bullshit) into a fantasy setting? Could it be that slavery during WWII isn't the reference they're using to construct the scene here? Have you even considered the fact that real slavery in Japan being not so distant DOES in fact add a perfectly reasonable scenario template to be included in modern setting manga and anime? That it doesn't even NEED to be "easier" to add because it was "only around 60 yrs ago?" Again dude, when they add this shit to an isekai or fantasy with medieval flair, it's not because they're thinking about slavery in WWII. Japan does not give a fuck about this in the way you think they do. Comparing it to American slavery is ridiculous.
At this point, I think it's far more constructive to agree to disagree.