It wasn't that long ago that people with mental problems were sequestered away in asylums where the conditions were often-times worse than the prison system. And many times the workers would abuse the patients (phsyically,sexually,etc) because there was little the patients could do (i.e. if she says that I raped her, I'll just say that she's delusional).

Is it any wonder, that other mental conditions aren't really taken seriously? For most people 'depression' is some nebulous condition that no one takes seriously until the depressed person has a failed attempt at suicide then everyone says that the "didn't see it coming."

Extreme difficulty of reliably diagnosing and assessing the impact of the illness on ability to work.

Prejudice.