The thing about a lot of people with severe(yet hidden) mental illness, is that they don't think they have a mental illness, and will not seek out help. Unless they're committing crimes, or are observed and reported by their inner circle, there's no way to parse them out. This guy thought he was basically God. Doubt he's picking up the phone to proclaim he's insane and needs help.
Mental health funding would go to people suffering from overt mental illness(schizo's n' shit), which isn't bad, but thinking it would stop a guy like this, who obviously could function normally in society until he finally snapped, is wishful thinking.
Sometimes there isn't a solution. Any one of us could go crazy one day, for a whole host of reasons. Having mental health centers at every corner will not solve that issue.