Context and perspective.
What separates the type of "masking/camouflaging" between a neurotypical and an autistic? As you suggest, both do this.
There is a stigma surrounding all things "mental health",...and most people in the general population know very little about how adult autism presents/manifests itself. That said, most neurotypicals know when behavior is "off",...and although they may not be able to articulate exactly what they are being confronted with,...the amygdala triggers their brain, and causes them to distance themselves from us. It's these reactions that contribute to poor job interviews, poor professional and social experiences, a lack of intimacy, further depression,...and even suicide.
Furthermore, if you were diagnosed as a child, and your parents made you go to "therapy",...basically teaching you how to hide your autism "for the greater good",...it sends a really bad psychological message. "YOU" are not acceptable in society,...so "YOU" have to change.
We all, to some degree, learn from assimilation,...observe and imitate, but a neurotypical is equipped with a rather "innate" or "instinctual" ability to do this,...and most autistics do not. The autistic typically has to think their way through it,...making it more of a conscious effort,...is open to "slip ups",...and can present itself as "fake" or "bad acting skills". It is mentally exhausting. Analogy: Your computer has a limited processing speed,...and if there is a background program running (the masking program), using a significant amount of that processing,...and you are trying to run another program (the social interaction program),...both programs may suffer slow processing. Welcome to the autistic brain. The neurotypical brain, one might say, has the "masking program" as part of the operating system, itself.