Social skills are instinctive to NT's; it's not something they have to think about. The social skills I've learned, which are woefully deficient, were acquired through painful trial and error. Though I can now do proper voice intonations, provided I'm not stressed; and I can recognize many non-verbal communications, also provided I'm not stressed, I'm still not good at it. I've also learned to detect most sarcasm, and even to return it.
Interacting with NT's requires that these things be processed instantly and subconsciously. I'm at my best dealing with these things when I have time to think about them, which normally isn't possible in social interactions. I think this is why I find most social interactions to be both exhausting and exasperating. Thus, I prefer to be alone, or to interact with others on the phone, or better yet, the Internet.