Earlier quoted context omitted.
> I learned that at least in Texas all plates are made by minimally paid prisoners Lol, wasn't slavery outlawed in the US, or were some states still allowed to keep it? That's absolutely bananas if true.
Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.
[1] the only excluded bit is the followup "Congress shall have power to enforce this article by appropriate legislation." Without this, the power to enforce the 13th Amendment would be left up to the states due to the 10th Amendment ("The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."), which would have slightly useless given the whole war that had just been fought over some states wanting to keep slavery.