Because it puts both parties at an uneven level. The, say, neurotipical individual* feels the sense to treat the autistic individual as "different". And the autistic person almost gets a carte blanche to do, in a sense whatever s/he may want. "Oh, well, s/he's autistic. I would never accept this behaviour de any other person", vs "I can be as quirky as I want, I said I was autistic ¯⁠\⁠⁠(⁠ツ⁠)⁠⁠/⁠¯"

If the subject comes up, sure, say it. If it is necessary, sure, why not. But for daily interactions? That's like me going around telling any person I meet, "oh, by the way, I'm a man". I mean, it's a fact; but it's not particularly relevant information when meeting someone.

What I'm trying to say is this: from my experience there is nothing wrong about the artistic people I've met. They tend to be slightly different in approach but that's not a problem to me as I adjust my personality to the person I'm interacting whilst staying myself. (I'm not going to talk to a mate the way I talk to someone I'm trying to have sex with. Basic example to prove a point.)

*The neurotipical individual may not even notice or find anything to be strange about the autistic person. Basically "you"'re saying: treat me different.".