A DM's job is to facilitate the world for the players to run around in. They can provide alternatives, pick at the desired themes to help get the player's idea across.
It's not the DM's personal private ground to run around in. If they want one of those, they should get into novel writing, not dealing with the fact players can and will disrupt their setting.
In the early days of D&D there was an almost punishing emphasis on DM control of all aspects of game play, especially the campaign setting. I think this was an inheritance from D&D’s roots as a war game variant, and perhaps also a result of Gary Gygax’s own controlling tendencies - or at least that was the impression I got from reading his rulebooks and magazine columns, which seemed to constantly urge DMs to bring the hammer down on those unruly, insolent players.
Today the pendulum has swung far in the other direction, and some players seem to think that the DM is there to cater to their whims in a “customer is always right” fashion. What happens if two or more players’ stories clash with each other? Some DMs would indeed probably be happier writing fiction, instead of running reluctant players through a pre-plotted railroad based on deep cuts of homebrewed lore. On the other hand some players might be happier trying out for amateur theater productions, where they might have a chance to be the actual star of the show. I would like to see a bit more flexibility and willingness to compromise on all sides of the table.
If you want to blame anyone for D&D being a grab bag, then you probably want to look at TSR putting cowboy gods and Barsoom encounter tables into Greyhawk, to say nothing of having Gamera and Aura Battlers hanging out in space. Grab-bag stuff like that is in this game's lifeblood from the very beginning.
I think it is pretty interesting that both Blackmoor and Greyhawk, the two original D&D campaign settings, each include gonzo crossover stuff like steampunk war machines and crashed space ships full of robots, laser guns, and bug-eyed aliens. S3
Expedition to the Barrier Peaks seems to imply that mind flayers are ETs who arrived on Greyhawk in that wrecked spacecraft, but of course that possible origin story has been overwritten by decades of newer lore detailing them as Lovecraftian body snatchers.
Also like, let's not forget one of Dark Sun's more popular races is a direct Forgotten Realms import. Thri-kreen aren't Dark Sun originals.
The Thri-kreen actually go all the way back to the early 1980’s, several years before FR replaced Greyhawk as the default setting for 1E. I remember seeing them in one of the 1982 AD&D Monster Card sets, and the art from those cards was the first thing that piqued my interest in D&D back in grade school. Those monsters soon appeared in hardcover in the 1983
Monster Manual II, but Thri-kreen remained somewhat obscure as I do not remember them being used much anywhere else in 1E materials.
Wikipedia and the Great Library of Greyhawk confirm that the Thri-Kreen were created for the second Monster Card set by Paul Reiche III, a childhood friend of illustrator Erol Otus who contributed to a number of classic TSR products like X1
Isle of Dread, the “A” series of AD&D 1E modules, and the Gamma World game. He is probably better known for his later work on science fiction CRPGs like Starflight and the Star Control series, so it is interesting to learn that he is a Jack Vance fan who created a D&D species that could have easily fit into SF or ”sword & planet” settings.
In any event, all of this only reinforces your point that the Thri-kreen became an important part of Dark Sun from 2E onwards, even though they were not originally created for that setting or edition. There are probably other examples of imported content becoming essential to various D&D settings if anyone cares to look. I would rather see people make these legacy settings their own and just enjoy playing with them, rather than trying to fossilize them in amber by fighting battles over decades-old canon.
