The "standard" in society is to be social. So if you appear to be less social than the norm, people don't know how to handle that. So you're weird, "think you're better than the others", or people assume they did something wrong causing that.
People just don't know how to deal with introverts. How many times, when I was younger, people would ask me "what's wrong" if I didn't want to go party all night long. Nothing's wrong, I just don't want to go party
And it's gonna get worse : in this age of sharing your life on social media and whatnot people feel entitled to knowing what you're doing, even more so in "liberal" jobs were the lines between personal and professionnal life are blurred. This friend of mine told me people at her former job felt some kind of way that she had a life outside of the job and didnt join at all post-work drinks/dinners. Another friend told me the same thing at an another job. Sometimes I myself would actually lie to people just to go home and chill lol.