Of course WotC worries about that, but their priority is the new generation. And that problem also happens with the rest of settings.
I have suggested in the past the option of alternate continuities or parallel timelines.
Other reason for the delay is if Hasbro wants D&D to be a multimedia franchise, then they have to talk with the movie producers to check what retcons or changed details are necessary. Maybe the screenwritters, people with higher profesional level, suggest new ideas, and someones are enough good.
And the metaplot is a double edged sword, because a good story helps to sell more, but also it starts to limit the actions by the other players, because if you want to follow the canon, then some things have to happen, but other don't.
Some things only need to be rewritten, for example the origin of the muls is not forced breeding, but genetic engineering, and muls can breed, but it is more difficult without the right "help" (medic therapy).
* Maybe a young adult player likes a daylight grimm tone to his stories, but a 12y player would rather more space for the hope. In my opinion the sorcerer-kings are going to fall, but not thanks a little group of heroes who save the day, but after a lot of blood, sweat and tears.
* DS may have got some elements seen as problematic for the standars of the current "sensibilities", but Warhammer 40.000 is grimmer and I don't see anybody reclaiming its cancelation.
Slavery is a common occurrence in the Known World and has been found among numerous civilisations throughout history. Slavery is widespread among the barbaric tribes that worship the Dark Gods. Among the people aligned to Order, it is a common view to regard all servants of chaos as slaves in...
warhammerfantasy.fandom.com
wh40k.lexicanum.com
* There is slavery in the Athasian city-states because usually there is in all the evil empires of the D&D multiverse.