Cross-posted from "It does indeed" by @LadyButterfly@piefed.blahaj.zone in !autism@lemmy.world
My kid was diagnosed as autistic at 15 because their therapist suggested getting them evaluated. They asked me recently why we didn't get them evaluated sooner.
After reading up about autism and talking to the therapist and reading the evaluation writeup, I realized that my husband, our other kid, my dad, and I are all definitely autistic, as is my step-father-in-law. A lot of our friends are diagnosed with some variety of neurodivergence (autism, ADHD, severe OCD), and probably some of the undiagnosed ones are also neurodivergent.
I told this to my kid and ended with, "So you seemed normal to us."
Obviously I don't have any insight in your case, but my guess is that a lot of parents don't consider that their kid might be autistic because they don't realize that there's anything unusual.