This probably won't be very comforting, but here's what I've concluded:
Important parts of social interaction occurs subconsciously. As someone with ASD, you can learn everything - how and when to smile, how much information to share, what topics to avoid - all of it. But you can't learn the stuff that happens subconsciously. Those tiny little micro movements, vocal inflections etc. that no one sees but that everyone feels.
So you can have a conversation which someone that plays perfectly, follows all the rules. And that person will still come away from that interaction feeling that something was off. And that reflects on the person they were talking to. They might not say so, they might not know it consciously, and they might not be able to say what it was but nonetheless they're left with a little niggling sensation that prevents them remembering the encounter as pleasant and wanting to do it again.
I think, with forced exposure (e.g. seeing people every day through work or some other necessary shared experience over time), it can be overcome and people will get used to us and start to appreciate the other parts of our personalities that make us people worth knowing.
But getting beyond that initial part, where they're not sure about us, it's what's hard. And why its so hard to make new friends.
That's what I think is going on.
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Naturally occurring variant. Swollen oafish and wince positive.