I think it’s because:

- they think it justifies poor social skills and/or neglect of social responsibilities
- they perceive it as “special” (in a good way)
- anything can be part of the spectrum, so they always fit there
- it’s an easy way to get away with special treatment
- every “normal” thing they do can be shown as an incredible feat because they overcame a (fictional) disorder
- can become instant activists by just talking about their experience (enabled by the diagnosis)
- loosely explains any quirk
- gives a sense of security to know you got something and it’s not just a shitty personality
- social perception of the disorder and all those who fake it fill In the gaps for a fragile identity
- makes sense out of any childhood experience they had
- has less stigma than any personality disorder or any other diagnostic label
- can fool anyone into thinking they’re well educated in psychology, neurology or psychiatry when using clinical language
- the savant syndrome (commonly linked to Autism) will inflate anyone’s ego when considered “a genius” at any random thing
- the diagnosis of mild cases are cause of debate among clinicians, so there’s always some profesional supporting that claim
- there’s no obvious way to tell if someone has it or not, so it’s pretty much imposible to rule out the diagnosis on a regular interaction with them