Maybe they need better treatments. Has anyone asked psychopaths - "How would you convince a psychopath like you to stop doing X?" Has anyone let psychopaths try? Aren't they the master manipulators? They even have a readily available model of a psychopath to test out the theory on. How convenient! Sufficiently motivating a psychopath with rewards for changing the mind of another psychopath might be an effective treatment for the first psychopath. Did they try that treatment?

Something like it was tried in Canada, in the sixties, with LSD, in a four year experiment where a group of 30 psychopaths were, at least apparently, temporarily reformed through unconventional means.

This strange and unique program was obliquely referenced in the top post:

...operated for over a decade in a maximum security psychiatric hospital and drew worldwide attention for its novelty. The program was described at length by Barker and colleagues…The results of a follow-up conducted an average of 10.5 years after completion of treatment showed that, compared to no program (in most cases, untreated offenders went to prison), treatment was associated with lower violent recidivism for non-psychopaths but higher violent recidivism for psychopaths.

The Insane Criminal as Therapist
E.T. Barker, M. H. Mason, The Canadian Journal of Corrections, Oct. 1968.

Here's an account from a recent pop-psychology book, The Psychopath Test:

In the late 1960s, a young Canadian psychiatrist believed he had the answer. His name was Elliott Barker and he had visited radical therapeutic communities around the world, including nude psychotherapy sessions occurring under the tutelage of an American psychotherapist named Paul Bindrim. Clients, mostly California free-thinkers and movie stars, would sit naked in a circle and dive headlong into a 24-hour emotional and mystical rollercoaster during which participants would scream and yell and sob and confess their innermost fears. Barker worked at a unit for psychopaths inside the Oak Ridge hospital for the criminally insane in Ontario. Although the inmates were undoubtedly insane, they seemed perfectly ordinary. This, Barker deduced, was because they were burying their insanity deep beneath a facade of normality. If the madness could only, somehow, be brought to the surface, maybe it would work itself through and they could be reborn as empathetic human beings.

And so he successfully sought permission from the Canadian government to obtain a large batch of LSD, hand-picked a group of psychopaths, led them into what he named the "total encounter capsule", a small room painted bright green, and asked them to remove their clothes. This was truly to be a radical milestone: the world's first ever marathon nude LSD-fuelled psychotherapy session for criminal psychopaths.

Barker's sessions lasted for epic 11-day stretches. There were no distractions – no television, no clothes, no clocks, no calendars, only a perpetual discussion (at least 100 hours every week) of their feelings. Much like Bindrim's sessions, the psychopaths were encouraged to go to their rawest emotional places by screaming and clawing at the walls and confessing fantasies of forbidden sexual longing for each other, even if they were, in the words of an internal Oak Ridge report of the time, "in a state of arousal while doing so".

...

Barker watched it all from behind a one-way mirror and his early reports were gloomy. The atmosphere inside the capsule was tense. Psychopaths would stare angrily at each other. Days would go by when nobody would exchange a word. But then, as the weeks turned into months, something unexpected began to happen.

The transformation was captured in an incredibly moving film. These tough young prisoners are, before our eyes, changing. They are learning to care for one another inside the capsule.

We see Barker in his office, and the look of delight on his face is quite heartbreaking. His psychopaths have become gentle. Some are even telling their parole boards not to consider them for release until after they've completed their therapy. The authorities are astonished.

Several of the 30 participants of the experiment went on to commit violent homicides some years after release.

An internal memo from the experiment: "LSD in a Coercive Milieu Therapy Program" (E.T Barker)

Intriguing.