There seem to be a lot of reasons behind the increase in autism diagnoses(vaccines not being one of them).
IMO, one of the leading reasons autism diagnoses have gone up is that the criteria for the diagnoses have broadened and awareness of the disease has risen.
Rising awareness may explain spike in autism diagnoses | Spectrum | Autism Research News
Adults are being diagnosed with the disease now. It's not as if they just developed autism. They have had it all their life, but they are only now being diagnosed with autism. What does that tell you?