With phones, and before that music, and before that newspapers, it's a social norm. If you are trying to talk to people you feel like the weirdo.
And I get it, cause I don't like making myself vulnerable. I wish I talked to strangers but it's hard to undo a whole childhood of "Don't stare, don't bother them, keep to yourself, everyone loves how quiet you are, you're so mature for your age because you never talk, etc."