Metaplot is RPG cancer!
Timeline advancements make settings unplayable, especially when they come in regular pieces. (If they come every 10 years or so, it's basically alternate versions.)
If a setting updates what happened to important NPCs, major locations, and ongoing regional conflicts, then I wouldn't want to have anything happening in my campaign now that turns out to contradict and be incompatible with what the writers announce officially happened six months from now. What this means in practice is that I can't use the major NPCs and conflicts in my own campaign. Any time a new update comes out, I still can't use it because I have to wait for the update after that, and that continues until the metaplot is officially wrapped up and concluded. At which point the conflicts ar no longer interesting and many of the NPCs gone.
Metaplots are the antithesis of RPGs.
A book for GM is supposed to provide hooks and let every GM run wild with it.