I actually did read the article. The article mentions one or two examples of mentally typical people who are homeless. Ok. I've dealt with many many more than that who are most certainly not University lecturers.
And if you can get that far, then perhaps you can see that the homelessness problem being described in this article goes well beyond the two causes you're trying to reduce the whole thing to?
She presumably has other options given her education, unlike other psychologically disabled people who have no other option but to live on the street. Of course pathological stubbornness could be a disability.