I think they just mean that it’s not necessary for playing the game. It isn’t like if you know the lore then you can find a secret cave, that gives you access to extra content. It is there for its own sake.
The value add that it gives is entirely dependent on the individual. It would be nice if there was some gameplay reward for reading it.
My company buys it. No idea what they use it for since I work in IT and I don’t use it for anything.