The reality of seeking diagnosis as an adult is that you get endlessly dismissed. I've been told I can't possibly be autistic because I can make eye contact, can talk, drive a car, or get to the appointment by myself. I've been misdiagnosed with and medicated for ADHD, personality disorders & OCD. The blatant incompetence of mental health professionals and complete lack of proper support and understanding drove me to the brink of suicide. So... yes, it's a bit of a selection bias, but the other option of searching at random - and getting hurt along the way - is just hell.

False positives are rare and inconsequential; false negatives destroy lives. It's as simple as that.