Does it? The alternative is non-profit incarceration/detention, in which the incentive is to not put people in prison, leading to more crime, lower trust and more victims.
How do you figure? Is the "I'll save you money by being soft on crime" election platform popular in your country?
With the added benefit of not costing the taxpayer as much.
You might argue that it drives efficiency but what does efficiency mean in the context of a prison? Cheaper food for the inmates? Less pay for the guards?