Mental health diagnoses pretty much only happen when the patient's life is impacted enough to convince the people involved in their life that there's a problem and figuring it out is necessary. If you get good enough grades, have a non-zero amount of friends, have a family and career that accommodates your random foibles, and generally manage your life well, then you can be as textbook mentally ill as you want without ever getting mental health professionals involved in your life.

As a relatively famous example, take Bill Gross, aka the "Bond King". He only realized he had Asperger's in his seventies when it was randomly the topic of a psychiatrist he was having dinner with. And why would he seek out some kind of diagnosis? He's happily married and running fantastically successful bond funds.