social interaction and small talk - why don't we learn?

One thing I was thinking about today was how so many autists have issues with small talk and social interactions on a day-to-day basis.

This is a common autistic trait and I myself have suffered from it but what puzzles me is how so many come to understand it, have the understanding and capacity to learn about it (mostly via the internet or books) and yet won't learn how  to develop this fairly simple skill.

Is it because the "rules" of small talk are too complex to learn? I've read up on the subject and am pretty sure this is not the case.

Is it a confidence issue, a fear of social rejection issue, a demand avoidance issue or what?

I realise that in the current social inclusive environment we should be accepted for our differences, but that isn't really a message the 98% of non autists seem to have gotten in my experience.

The skills are pretty basic with straightforward rules so you would imagine this is right up most autists street yet some of the most capable autists I hear from here can't seem to come to grips with it to use it effectively.

I'm curious to hear your own thoughts as to why any of you still struggle with this.