Honestly, it's supposed to be in your words but I'd say the reason they do not see it is because they cannot read or sense mental or emotional health. They can SEE psychical health. Like if you fell and broke your leg, you'd have a cast on it. They cannot see mental and emotional health because in order for them to that person would have to reach out to them or show severe symptoms. But even then, if they're not a professional, they might not see it.
Some severe consequences could be: That person taking their own life. Not being in a good mental state which can affect their body and way of thinking. And, not being in reality anymore.