If you start a new job and on your first day they go "Yeah the last guy said we don't need a database, so he rolled his own." are you gonna be excited, or sweating?
Exception being perhaps "The last team chose to build their own data layer, and here's the decision log and architecture docs proving why it was needed."
That said, there really are good use cases for readable formatted files. For example configuration files that are checked into source control are far more trackable than a SQLite database for the same purpose. For another example, the files are convenient for a lot of data transfer purposes.
But for updateable data? You need a really good reason not to simply use a database. I've encountered such edge cases. But I've encountered a lot more people who thought that they had an edge case, than really did.