But the political situation that allowed for the backdrop in Raiders of the Lost Ark only lasted for a scant few years, 1933 to 1939 (the period from the Nazis seizing power in Germany to the start of WW2). After that, the world changes significantly which invalidates many of the stories you could tell. Now, that opens up a whole new bunch of stories, but if you were attracted to the world because of its 30s pulp feel, and it then turned into a world war you'd get quite disappointed in the setting's caretakers.
It does not change the fact that the Raiders of the Lost Ark is not a true story. It did not really happen. And yet Spielberg was able to "somehow" fit it into the real world history. I know, right? And this happens all the time - all these stories set in different parts of our "living" world.
But if I don't like the direction in which the developers are taking the setting, that makes future supplements unusable to me. And this is not some hypothetical scenario - it's one I've personally encountered in the Realms. I thought the description of Tethyr in the 2e FRCS box sounded like a very fertile setting for adventure (country torn by civil war for 20 years, so each little plot of land has its own warlord/baron that can send adventurers off to do things, or maybe the adventurers are just looking out for the common man), so I bought Lands of Intrigue, the boxed set that covered Amn and Tethyr. But the Tethyr in that box was very different from the Tethyr portrayed in the FRCS - now the civil war was over, and a rightful king along with a far more capable queen had returned and put things in order again. And all of that stuff had happened in a novel trilogy.
Ok, so you dont like the way a living world goes. I get it, it happens, the Spell Plague is a thing for me too. But there is nothing worse then a world stuck forever in a lump of amber never growing never changing. Sure it is easy for the writers but what would the Harry Potter books have been like if he was stuck as 11 years old all the time like some kind of English version of Bart Simpson. What about Dragonlance where we get one whacky adventure after another of Raistlin and friends who never achieving anything of note.
Another issue is that it often creates a very weird, unstable world, because the metaplot machine needs fuel. Just look at the period of 1357 to 1372 DR (15 years, the period between the 1e FRCS and the 3e FRCS). In that time, the Realms have had these things happen:
* The ancient god Moander rising again, but being banished.
* The Time of Troubles, where a few gods died (notably Bane, Bhaal, and Myrkul), a few new ones ascended (Cyric and the new Mystra), and a few gods disappeared (Waukeen).
* Invasion of the Tuigan horde (essentially the Mongols).
* Maztica (America) discovered.
* The reclamation of Tethyr.
* A plot by the new god Cyric to mind-control people into worshiping him, which backfires and leaves Zhentil Keep in ruins and causes him to lose the portfolio of Death to the new god Kelemvor.
* Daggerdale is liberated from the Zhentarim who were occupying it.
* The goddess Waukeen is liberated from her captivity in the Abyss by a band of adventurers, and she returns as the Goddess of trade and wealth.
* With the help of an artifact provided by Khelben Blackstaff, Fzoul Chembryl manages to release Bane's demi-god son Iyachtu Xvim from a prison beneath Zhentil Keep, and have him claim the portfolio of Tyranny from Cyric and become a lesser god in the process.
* As fallout from the previous point, the Harpers split because the leadership did not approve of Khelben providing Fzoul with said artifact.
* Manshoon, the leader of the Zhentarim, is killed by Fzoul Chembryl as part of the latter's effort to take over the Zhentarim. Somehow his Static Clone spell (which created a bunch of backups for him) got messed up, and all the clones activated and started fighting one another to the death. One of them got vampirized.
* A dragon leads an army of orcs and goblins in an attack against Cormyr, but is repelled. King Azoun IV dies in the process, leaving his young son Azoun V the nominal king, but the country lead by a regent.
* Mulhorand invades and conquers Unther.
* Turns out Bane was using his son Xvim as an incubator of sorts, so Bane returns (killing Xvim in the process).
* A flying city full of ancient archmages that went on a tour of the Shadow Plane in order to avoid the destruction of Netheril reappears.
* The town of Tilverton, near Anauroch, was destroyed by some unknown magical force but that seemingly had something to do with shadows.
That's a lot of stuff happening in quick succession. For someone jumping in at this point in the setting's history, that's a lot of recent events to take in and try to make sense of - and that's another problem with metaplots: they make it harder for new people to become accustomed to the setting, because they can't just get the core book and some random sourcebook. Because the sourcebook will probably refer to a bunch of stuff that happened in between the release of the core book and that particular sourcebook, and the new customer will go "What the heck is this? Why are they talking about the Banedeath a lot - there's nothing about that in the core book? Is that something I'm supposed to know about? Screw this, I'll go back to Diablo."
Are you really telling me that an unstable world is a "bad" thing for an adventure game like DnD? What do you call the current batch of adventures - a quiet time on the Sword coast?
I dont follow WoW at all but I think I would be safe in assuming that someone could make a very similar list of stuff that was happening in the MMORG. Does all of that stuff also make people want to quit and play Diablo? I guess Diablo is great for those type of players who just enjoy endlessly repeating the same story over and over. Which is why you have different games that appeal to different markets.