I don't think there's any specific reason for people to want the reason to be tylenol specifically, but RFK had announced that he was going to solve autism by September and it seems like he really just wanted to come up with an explanation for autism that blames it on some sort of medicine that people can simply choose not to use. Tylenol is something that people have considered as a possible cause of autism, although the best/biggest study seems to have pretty clearly proven that use of tylenol doesn't actually cause autism, so it's a fairly obvious thing to pull out if you just want to come up with some medicine to blame for autism.
Perhaps the better question is why he isn't blaming vaccines, which is what many people expected him to do, but maybe there was too much pushback from the rest of the administration on that.
He promised us "the" cause of autism. What we've gotten, even in the purchased expert testimony, is a minor contribution to autism at best.
So are we still waiting for the big news about what really causes autism? Everybody assumed he was gonna say "vaccines". He's got another week to go. Is this all we're going to get, or is there more?
Perhaps the better question is why he isn't blaming vaccines, which is what many people expected him to do, but maybe there was too much pushback from the rest of the administration on that.