what advantage in communication does it have over "not autistic or aspergic"?

It is one word not four. Humans always invent jargon terms if they are in a subculture that requires repeated reference to a specific concept.

It also allows to some extent to include the not-bipolar, not-ADHD things by default which is useful. Because it is easier easier to have general discussions about category if you can conveniently eliminate most of the outliers.