It depends. Some are owned by the state. Others are owned by private for-profit companies which sign contracts with the state to guarantee certain occupancy rates for the duration of the contracts or to guarantee certain profit margins.

Of course, since these private prisons profit off of people being incarcerated, they have every incentive to lobby for tougher drug laws, mandatory minimum sentences, three strikes laws, etc. And they have little financial incentive to rehabilitate inmates since a high recidivism rate just guarantees future profits. It's horrible.

Not to mention that states get stuck in a situation where if they were to pardon all low level drug offenses, for instance, they might end up freeing too many people and be in violation of their contracts with for-profit prisons.

Shitty programs like this tablet program up getting used by the state prisons too. It's not just private prisons.

What ends up happening is that we incarcerate far too many people and underfund the prisons. These private contractors come by and offer to provide a service for a fee, then give the prison a cut of the profits. They've then been known to petition to become the sole of that service too. Not sure how this will work out in terms of this tablet usage and reading, but in the past there's been at least a couple of jails that tried to cut out in-person visits entirely in favor of paid video conferencing, even when both ends of the conversation are in the same building.