I really don't think there's any deeper meaning behind why autism is being LARPed as so much, it's just the flavor of the month 'quirky personality trait.' Same way everyone identified as bisexual for a while, then bipolar, then DID, etc. In a couple months the novelty will run out, because if everyone's special then no one is special, and there will be a new Tik Tok trend.
E:
You're not wrong but this is a dumb take. Obviously people who are severely mentally ill will show more physical signs, because their illness is severe. If that's all doctors had to go off on, then 90% of mental illnesses would not be diagnosed altogether. There are plenty of methods to sus out fakers, that's why these people study human behavior and the diagnostic criteria for decades. I'm sure there's plenty of cases where even psychiatrists were successfully fooled and manipulated by fakers, as they're humans and not infallible machines. But you'd be hard pressed to find a group of psychiatrists struggling to diagnose someone based on arbitrary shit like "well most autistic people have ears half an inch shorter than non autists, have you measured their ears?" instead of like, you know, just observing how they behave.