> You’re not interrupting my focus for me, you’re doing it for you.

While it may be selfish and pointless, it's the default expectation that in public space people can be spoken to, but it costs something to remove that possibility without also physically isolating oneself in some way. Not all public space is necessarily social, you can be alone in a wooded glen which creates a proximity barrier, but trying to preserve your whole private sphere while being in an otherwise potentially social space removes something from that space.

When I deliberately don't want to chat with anyone, I just take a side street or something. Not always possible, but it's rarely worth it; usually work is the semi-public space I'd prefer unbroken focus.

I do think it's overblown to make some grand statement about this behavior if it's only an occasional thing, but if the default expectation shifts to people hesitating to talk to people only because they might have headphones in, I think we've lost something.