The problem with giving honest-to-god Truths in game books is twofold. First, the players will dig them up, in which case they either gain the free "Plot Omniscience" ability, or else the DM has to rework the campaign, therefore losing any benefit of having "the full truth" in print.
Second, metaplot heavy books, especially ones that tell the full truth and nothing but, encourage a "must buy every book" mode of thinking, as well as a "can't deviate from canon" mentality. Both can get quite annoying to non-obsessive gamers, even if they're hard habits to shake. Note how 3e made a point of not following a 2e path on this.
(And Forceuser, how can you like the Shadowrun approach? I personally like the game, setting, and most of the time mechanics a lot myself, but referencing another book in the core book? Forcing you to buy other books to understand the huge bombshell they dropped in the new edition? Forcing you to buy a splatbook you may not want/need just to understand what another referrs to? Thank you, but that's not my cup of tea.)