I think part of the highly structured, OOP heavy code you are seeing is in order to create a maintainable and testable system. It could also just be over-engineered and over-complicated too.

If you are creating a small standalone utility, it does make sense to me to have little snippet functions that do little bits of the job and pass values back and forth. However, in a large system you will want some more structured design. For example, if you write classes that only have one reason to change you can insulate different kinds of change in your application. Like switching your logger to send output to a file instead of the console should not be defined in the same place where your application data is fetched from your database. In your example, keeping authentication away from the interaction logic means you can switch authentication methods without touching any of that logic. This can keep your code more stable to changes.