I imagine part of the problem lies in a deep-seated prejudice that books which tell stories with pictures are intended for children, to help them form associations between images and words and to hold their interest while they learn to read. After you gain a certain level of reading competence the pictures get taken away and you’re supposed to rely solely on the words. An adult who enjoys reading books with pictures is seen as regressive or backwards in some way.
Another factor is that a lot of comics tap into adolescent experiences and fantasies: - There’s the normal guy with the secret identity and the unobtainable girl who can’t see beyond his geeky persona and is in love with his heroic alter ego. Or the disaffected loner, shunned by his peers but who has exceptional powers and a gang of cool super friends who understand him. This feeds into a perception that if you read comics you haven’t outgrown your teens and are an adolescent trapped in an adult’s body.
I didn’t begin reading comics until I was 19 so naturally I don’t regard them as something to be exclusively enjoyed by children and teenagers.
It’s blatantly obvious to anyone who spends more than a few minutes in my company that I am deeply uncool. I don’t think admitting to a love of comics would make much of a difference either way.