Private prisons represent only ~8% of the US state & federal prison population[0]. Private prisons, while bad, are a distraction from the larger issues of policing and incarceration in the US and aren't the reason why we have so many people locked up. Almost half of all federally incarcerated people in the US are there for drug-related offenses[1] thanks to the "War on Drugs", that's where you want to be focusing your efforts on change.
While that percentage is low, it doesn't tell the whole story. Private prisons are certainly a major symptom of the problem with our prisons. The U.S. has the largest private prison population in the world, and you'll note from your own link that the private prison population from 2000 to 2019 increased by 39%. Also, for federal prisons, the percentage of inmates in private prisons is 19.1%. These are definitely problems and discussing them also helps discuss the big issues such as why in the hell we're incarcerating so many people.
https://www.sentencingproject.org/publications/capitalizing-...