it is just that the first one is basically giving you the answer as opposed to you to be able to figure it out based on dialogues and random books/notes in the games, and I can tell you it is pretty satisfying to have this uncomfortable feeling of having unanswered question which finally you can find answers for after investing decent amount of hours (or using Wiki after giving up which is fair). As I said, the way Swen designs games, he want you to dive deep into this storytelling and you need to figure it out yourself.
Both things are not mutually exclusive.
You can have exploration AND a codex. You simply don't fill the codex completely from the beginning of the game.
If you start off with a basic codex full of stuff your character should know (It's always kind of silly that you play a character who lived in the region until adulthood but don't know the most basic things...) but further details must be uncovered before they are put in the codex.
I've played some games that did this, where the text pop-ups in chat simply said "????" until you had discovered through dialogues and lore notes about the faction in question (With the details shifting as you discovered more information over time)
Think of it more like a journal that your character is writing down details in as they discover them, rather than a meta-game codex full of all the answers from the get go. So it doesn't replace exploration, but simply allows you to refer back to things you've discovered (Whilst providing access to those unfamiliar with the base level lore from the start)
