I think a lot of people have preconceptions about who is homeless and why. This man probably breaks that mold for many which is what makes this a story.
He is an addict, and that almost certainly keeps him out of shelters. He struggles with mental health issues. While he is smart and educated, those 2 things have probably made it hard for him to hold a job.
I am only surprised that anyone would think an Ivy League degree would confer immunity from this kind of problem. I have had a handful of friends with these “excellent credentials” take their own lives and we hear of students at top schools doing the same. That’s another riff on this story. He sounds like he still has hope.