nice ?

The isekai authors' endless fascination with slaves.

Yeah, the slavery thing is a staple of the genre I guess, for better or worse. Imagine the editorial meetings.

"So, I think your story is going perfectly so far. It's 100% generic isekai. Just what our customers have come to expect from us."
"Oh, uh, thanks?"
"But the cast is a bit light on slave girls."
"What? But there's like ten of them-"
"Yeah, you need more slave girls. Just make sure they're some fantasy race. Animal ears, maybe a tail. The readers really eat that shit up."