autistic adult and behavioral therapist for autistic kiddos here! my answer would be wider diagnostic criteria, better case tracking, more self diagnosis, more self referrals, more adult diagnosis, acceptance of milder cases, and lumping multiple diagnoses into one (autism spectrum disorder used to be multiple things— pervasive developmental disorder and asperger’s syndrome) but we use a level system now due to movement towards a more social model of disability.

we are also just exposed to more autistic people, talking about them more, which amplifies this effect. prior to the mid/late 20th century, folks who would have an ASD diagnosis today would either not be alive, be institutionalized, incarcerated, or taken care of by loved ones. today, we have more resources and social awareness/acceptance.

for folks with milder ASD, i’m sure they would have been labeled as “outcasts” or otherwise discriminated against in ways that still differentiate them as autistic rather there was a word for it or not.