I'm sure that there are far too many use cases of varchar(255) out there for anybody to deprecate such a feature without causing huge pain to everybody involved

I'm sure that there are far too many use cases of varchar(255) out there for anybody to deprecate such a feature without causing huge pain to everybody involved. Just look at the python 2 to python 3 transition, which is still ongoing, more than 10 years after the python 3.0 release. Also, warnings usually simply don't work. Developers or admins google the warning, see that it can be switched off, and switch it off. DDL is often generated (for example for migrations), and you might not want to add a special case for postgres if you can avoid it. Suppressing a warning is definitively easier than changing code generation in potentially non-compatible ways. Plus, I haven't looked it up, but given how prevalent VARCHAR(N) is, it might be part of the SQL standard.