While budgetary issues obviously play a part, as reported by the Houston Chronicle, the major reason may be that the programs do not work, as posted about previously.
Studies reporting success should be examined for the rigor of their evaluation, which should include third party evaluators, using a control group, and random selection—of sufficient numbers—and examining results after proper length of time away from program (3 years is a minimal standard).
An excerpt from the Houston article.
“DALLAS — When John Patrick Barton was in prison on his third drunken driving conviction, he was not among the thousands of inmates nationwide who undergo alcohol and drug treatment behind bars each year.
“Fifteen months later and out of prison, Barton is accused of driving drunk again. This time, authorities say he plowed his car into another, killing a woman and her teenage daughter in a Dallas suburb on Easter.
“Barton's case has turned into a rallying cry in Texas, where state officials have proposed slashing more than $23 million from in-prison treatment programs. These types of programs — many already stretched thin — are increasingly endangered as shrinking budgets force several states to consider cuts to treatment for drug users, drunken drivers and sex offenders.
“Though Barton was never ordered to undergo alcohol treatment after his third drunken driving offense, those opposed to the proposed cuts to the nation's second largest prison system are using his case as an example of what they fear will happen if treatment programs are trimmed.
"People say, 'How can you afford to (fund) this?'" said Texas Sen. John Whitmire, chair of the senate's criminal justice committee. "My comeback is, 'How can you afford not to?'"
“Studies have shown offenders with substance abuse problems are more likely to return to prison without treatment. Yet only 11 percent of the nation's inmates with substance abuse problems receive treatment during incarceration, according to the National Center on Addiction and Substance Abuse at Columbia University.
“Several states have already decided to reduce in-prison treatment programs that are often required as a condition of parole and can sometimes lead to early release from prison. In some cases, experts say, offenders may end up serving more of their prison sentence if budget cuts make it difficult to receive treatment.”