I know it's easy, but there's probably a long wish list and it's just not at the top. Other features like saving / reloading characters at creation, modifying the portrait from the game, and so on, must be in higher demand. The idea of having to write down notes may even scare away 99% of players, who'd rather have the thinking done for them.
I don't believe the developers explicitly wish not to have such a feature, it's a long game and it's not so much a problem of attention than a difficulty to remember all the details, especially if you can't play it in one weekend. What they probably don't want to have is a journal that literally says "go to <location>, talk to <NPC>", but that's different. If the players jot down a few notes, they processed the information themselves.