A lot of PWS are covert stutters. They’re able to hide their stutter in everyday life by constantly substituting words or just being quiet and pretending to be introverted. I was a covert stutterer for most of my life until I just couldn’t stand it anymore (it was utterly mentally and emotionally exhausting and made me feel fake and inauthentic). Since I’ve started joining stuttering support groups I’ve met loads of people whom I would’ve thought were fluent if we had had a short conversation in everyday life. That probably explains why it feels a lot less than 1%. The ones you do see are those with a stutter that’s too prominent to hide, or they’re people like me who can’t give a f*** about hiding anymore. It’s the same reason there seems to be fewer LGBT people in countries with anti LGBT laws and cultural mindsets. People will go to extremes to hide something they’ve been made to be ashamed of. But they’re still very much there.