It is arbitrary but so far as it is my own, it is also most people's, tying into my point about clarity of definition. Chattel slavery means the public acceptance of slavery--slave markets, the fugitive slave act. Chattel is a legal term connoting legal approval of slavery.
It is also what people think of first when someone starts talking about slavery. Alongside chattel slavery was indentured servitude, which might well fall into your definition of slavery.
>You're trying to claim that slavery doesn't exist because you want to make it be only something exactly the same as plantation era slavery
No, I am not. I am asking you to be more precise in your language, because typing off a one-line post about non-hypothetical slavery was confusing. Notice how more people upvoted you when you were expanded the precision of what you meant by slavery?