Earlier quoted context omitted.
The 1970s were 50 years ago. "Long dead", in other words. Did you know that Brazil didn't abolish until 1888? They also imported far more than the US: https://www.slavevoyages.org/static/uploads/01.jpg
And does Brazil have their own 13th amendment that allows them to use prison labor as their modern slave workforce?
...
Most countries’ legal systems, however, carve out an exception for prisoner-workers, permitting the state to require them to work—sometimes for no pay, but typically for very low rates of pay.
There are, even so, multiple potential benefits to prison work. For example, ICPR’s recent research indicated that prisoners who could not work (when prison regimes around the world were restricted during the COVID-19 pandemic) reported many negative consequences, including to their mental and physical wellbeing. At the minimum, work may mitigate some harmful impacts of imprisonment. At best, it may increase prisoners’ prospects of successful reintegration into society, potentially also benefitting society by reducing recidivism."
https://www.prisonstudies.org/sites/default/files/publicatio...
(emphasis mine)
Here's a photo from a Brazilian prison from Wikipedia: https://en.wikipedia.org/wiki/Penal_labour#/media/File:Inmat...