Sometimes it's used by the state itself for cost savings, as in California under then-attorney general Kamala Harris (now Vice President):

> “Extending 2-for-1 credits to all minimum custody inmates at this time would severely impact fire camp participation — a dangerous outcome while California is in the middle of a difficult fire season and severe drought,” lawyers from Harris’s office wrote in a filing.

https://www.washingtonexaminer.com/politics/kamala-harris-of...

The benefits of reduced labour costs are the middle class.

Similarly the middle class benefits from the lower working class wages that come from exploitation of illegal immigrants.

Well, the upper middle class who have higher tier jobs. Not the working middle class. (In USA everyone is "middle" class, because most are too proud to have class consciousness.)

The shareholders for the private prisons in which they are incarcerated: https://www.currentaffairs.org/2020/10/how-private-prisons-p...

:(

“In 2015, just 8% of the nearly 1.53 million state and federal prisoners in the U.S. were in private facilities” [0]. Prison slavery is not concentrated in and won’t disappear by closing private prisons. [1]

[0]https://www.pewresearch.org/fact-tank/2017/04/11/u-s-private...

[1]https://corpaccountabilitylab.org/calblog/2020/8/5/private-c...