I think it's just societies general view that humans need connection and everyone should be up and outgoing all the time, when really that isn't the case at all. If you're not outgoing, they think that you're just unhappy, and that is frowned upon. I feel ya. I'm the same way. I'm a little better in group settings but even then I'm shy/reserved/quiet. People always ask, "What's wrong?" I say nothing and move on my merry way. If they don't want to believe me, that's their choice but I don't have to justify myself to them.