Firstly because it's not useful to me, second because I don't like the idea of being defined in terms of it or treated differently, third because my school days were when I would have benefited from it but my teachers were understanding anyway usually. Even if they didn't know about it, they still figured out there's something not right when this kid has breakdowns in cooking class because the instructions weren't specific enough. Fourth is because it has never negatively affected me much academically speaking. It only affected me on a social level and even then I still had friends. And lastly but mainly, because as I said I've worked pretty hard to get to the point where it's not noticeable. I score more highly than most autistic people on the AQ (autistic-quotient test) but I don't think you'd know that from my behaviour, only if you asked me about how I think about things, which is something I can't really change and am comfortable with that. Maybe people know I like flags, but I've learnt not to ask strangers to ask me to describe the flag of Vanuatu or Nauru, lol. I don't even know if I would now be diagnosed since I don't let it affect my behaviour in significant ways. I hope that makes sense. Oh, and maybe this is strange, but my parents both worked with children and had children from previous marriages, so they were understanding and knowledgeable about development conditions. As a result, I've usually had support when I've needed it, and managed without it when I've needed to. Oh, and nowadays the reasons OP mentioned are relevant, too. I roll my eyes when people make ASDs a part of their problem (unless they really are severely autistic and don't know better). There are other quirks in my brain that I also don't talk about, since people won't believe you, or will assume you're using it to impress them/to get sympathy, etc. These are things I've learned and come to accept.

Sorry for the long message.