If you don't know how to use a database for whatever reason and are doing something as a test-of-concept then CSV is fine. But for anything serious - databases, particularly older featureful ones like postgres, have a lot of efficiency tricks; clever things like indexes and nobody has ever come up with anything that is decisively better organised than the relational model of data.

If you use a relational database, the worst-case outcome is you hit tremendous scale and have to do something special later on. The likely case scenario is some wins from the many performance lessons databases have learned. Best case outcome is avoiding a very costly excursion relearning lessons the database community has known about since 1970 (like reinventing transactions).

Managing data with a csv (without a great reason) is like programming a complex GUI in assembly without a reason - it isn't going to look like a good decision in hindsight. Most data is not special, and databases are ready for it.

Reliability, atomic updates, roll backs, proper backups, history management, proper schema, etc.

High-quality software which interacts with real transactional SQL databases is readily available, free, and easy to use. Building an inferior solution yourself, like a CSV-based database, doesn't make your product any better. (If anything, it will probably make it worse.)

It was never suggested to use a csv database, it was suggested that for small amounts of read only data a csv or other format file is a better option and I agree.

A quick rundown https://sqlite.org/aff_short.html