After hinckley, NGRI became very hard to win. As it stands today, less than 1% of cases that go to trial involve an NGRI defense. And of those, yes, they are very hard to win.
In fact, if you have time, I urge you to check out the case of Ralph Tortorici, which was covered by PBS (
link ). It was an extremely tragic case, where, imho, justice was not served. Importantly, it clarifies just what NGRI cases are actually up against.
That said, imho, the primary problem is, people often confuse mental illness with legal insanity. Our prisons are full of mentally ill criminals who do not meet the criteria for legal insanity.
Even so, arguably, the conditions exacerbate their illness, which in turn, imho, plays a role with increased risk wrt recidivism.
Still, our society, specifically, the american society, tends to strongly hold the eye-for-an-eye mentality. So, you end up with states abolishing NGRI completely, while forgetting the reason it exists in the first place.