I can't stand the term "mental illness." Why do we call mental suffering an "illness?"

I have depression. I'm a bit of a neurotic person. I have anorexia. I am high functioning autistic. Why do we call all of these things an "illness"? Mental illness is such a misleading term, it's like calling a heart condition a "heart sin" or a physical disability a "weakness." It gives people the wrong impression of how their suffering is their fault.