It's not nearly that simple. In a nutshell, their brains are very noticeably different from normal brains, the track record of treatment has been not only ineffective but sometimes counterproductive, and the problem is considered by many to be intractable. The studies done were not done well, and there have been some promising results with "decompression treatment" for juveniles who are mild to moderate in their psychopathy, and no other group. It would be a great boon to society if adult psychopaths could be rehabilitated, but no one knows how to do it.

I encourage you to peruse the whole thing if you have time, but here are some excerpts:

Putting these results together begins to paint a picture of the psychopathic brain as being markedly deficient in neural areas critical for three aspects of moral judgment: 1) the ability to recognize moral issues; 2) the ability to inhibit a response pending resolution of the moral issue; and 3) the ability to reach a decision about the moral issue. Along with several other researchers,149 we have demonstrated that each of these tasks recruits areas in the paralimbic system, and that those precise areas are the ones in which psychopaths have markedly reduced neural activity compared with non-psychopaths.

What does all this mean? First, it suggests that the story of psychopathy is largely limbic and paralimbic rather than prefrontal.150 This dovetails nicely with the central paradox of the psychopath: he is completely rational but morally insane. He is missing the moral core, a core that appears intimately involved with the paralimbic regions. If the key to psychopathy lies in these lower regions, then it is no mystery that the psychopath is able to recruit his higher functions to navigate the world. In fact, when he gives a moral response, it seems the psychopath must recruit frontal areas to mimic his dysfunctional paralimbic areas. That is, the psychopath must think about right and wrong while the rest of us feel it. He knows morality’s words but not its music.

The received dogma has been that psychopathy is untreatable, based on study after study that seemed to show that the behaviors of psychopaths could not be improved by any traditional, or even nontraditional, forms of therapy. Nothing seems to have worked—psychoanalysis, group therapy, client-centered therapy, psychodrama, psychosurgery, electroshock therapy or drug therapy153—creating a largely unshakable belief among most clinicians and academics, and certainly among lay people, that psychopathy is untreatable, though as we will discuss below few if any of these studies were properly controlled and designed.

Most talking therapies, at least, are aimed at patients who know, at one level or another, that they need help. Psychotherapy normally requires patients to participate actively in their own recovery. But psychopaths are not distressed; they typically do not feel they have any psychological or emotional problems, and are not only generally satisfied with themselves but see themselves as superior beings in a world of inferior ones.

Treatment not only seems not to work, there is evidence that some kinds of treatment make matters worse. In a famous 1991 study of incarcerated psychopaths about to be released from a therapeutic community, those who received group therapy actually had a higher violent recidivism rate than those who were not treated at all.

The state of the treatment literature has been described as “appalling.”

Second, and most importantly, the decompression treatment was highly effective in reducing both institutional misconduct and recidivism, but only if it was lengthy and only—and here is the less promising aspect of the study—for juveniles scoring in the low to moderate ranges of the PCL-YV (≤ 31)