I am saying this as someone with crippling social anxiety... I don't think they mean it out of active malice most of the time. They're just clueless and don't know how to react. They're not not the masters of social interaction they're made out to be, no one is! We're all just bumbling clowns on a circus planet
Neurotypical people have a secret, special way of saying "...okay." that saps all the joy from your body and makes you feel like an idiot, and they love to use it when you show them something you're really, really excited about