A high percentage of convicts are not in jail for violent crimes. Mandatory minimums means the judge can't decide what the sentence should be even if in the particular case, it would be worse for society if the offender was put in jail. For example if the offender was a person who otherwise made positive contributions to society, a volunteer, charity worker or someone whom people need, parent, etc.
Some fine people, distinguished physicists and doctors, are drug addicted to opiates. But their work is not impaired by a private problem they have, addiction. If they are arrested for it, under mandatory minimums they must go to jail, carte blanche. Could be the greatest person in the world in every other way.
Can someone explain Why they should go to jail, in any case?
Second the privatized prison industry commands billions of dollars, and jobs in support industries around it. There is a possible conflict of interest when it is a "growth" industry, just as shareholders demand increasing growth in any business, to make profit.