If you imagine neurotypical and autistic as two "languages", then masking is when an autistic person is going to the effort to speak the neurotypical language, so as to remove the burden from neurotypical people of having to parse the autistic language. Most of the time, unless the interaction is very short and one-shot, the autistic person will still come off as speaking the neurotypical language "as a second language" rather than speaking it "fluently"; but it is the lived experience of many autistic people that this is still less disruptive in mixed company than just letting go and going full native autistic and expecting neurotypical people to be the ones to adapt. (Even in SF, a randomly-selected group of people often contains a few people visiting from elsewhere, who have never interacted with [non-masking] autistic people before, and so have never learned to "speak" autistic.)
Which is not to say that it isn't nice to find other autistic people to hang out with, where you can just let your hair down and "speak your native language" together! But it's not like this is something people avoid doing, if they get the chance. It's just that in most places in the world, you're rather unlikely to stumble into groups consisting solely of autistic people. (Except maybe in engineering-led tech companies!)