If vaccines don't cause autism, then why does the diagnosis for autism keep going up? 1 in 100, 25 years ago, now it's 1 in 31. What is happening?

Watching a video where someone autistic gets a speedrunning world record and their parents celebrate with them, and getting emotional cos the parents probably wanted to celebrate something, *anything* with their kid and see their kid achieve *something*. And a speedrun world record doesn't really change much in real life but it's still an achievement that the parents can finally be proud of their kid for