I do see what you mean but again I'm not sure if I buy it, because it still sounds pretty meritocratic. I have been through times in life with severe social anxiety and times without, and the quantity of approach hasn't really changed. And doesn't explain the people who get approached even when trying to be closed off (I mean just listen to women complain how they're constantly hounded by men no matter what they do).
Also, what about neurodivergent people who may express their openness/closedness somewhat differently? Are they screwed no matter what?
I won't say you can't do anything to influence your approachability, but I really do think there is a very large component which is essentially fixed, and people rarely acknowledge this (which is annoying).
It's not fixed. It's like anything hard that doesn't come naturally. You may wish you were a guitarist, but actually playing guitar well is really hard. You have to work at it, over and over, for months/years. But if you can move your fingers, you can learn to play guitar. It just won't come quickly or easily, and you may decide you'd rather skip it.