Because there has been an emphasis on de-institutionalization of the mentally ill for decades, even though the Riverview site still exists and could be reactivated at any time if the will existed. When psychotropic drugs like Thorazine came along in the 1950s, earnest reformers dreamed of a day when the mentally ill could live at home, kept under control by medication. Of course, if they're not in a hospital, there's no one to make sure they actually take it. The result is that the ones who don't end up on the street, self-medicating with smack, crack, and airplane glue.

Re-institutionalization is the obvious answer; it would get these people off the street and back on to the medicine they need. But the government, fearful of liability thanks to multiple cycles of lawsuits for past abuses, has no desire to head back down that particular rabbit hole. The result is that these people are "cured" when they finally OD, or wig out so badly that the police have to shoot them.