Autism has been trending lately. A similar trend occurred with bipolar disorder; nearly 100% of people in rehabilitation clinics have this diagnosis. The most likely reason for this trend is insurance fraud. An insurance company will pay more to treat a suicidal bipolar autist then they will to treat an addict with a transient anxiety disorder.
Another factor is patient expectations. When a parent or patient pays for a psychiatrist, they expect a diagnosis. They don’t want to be told that they are normal and fine.
It’s possible, but the psychiatrist has a strong financial incentive to give a profitable diagnosis. Since there isn’t any consequences, why wouldn’t they? What do they care if their patient ties their identity to a lie or becomes addicted to amphetamine?