Why would you think it's fair or reasonable to tell everyone else that they do need a trope because otherwise their worlds won't be as realistic or as rich?
"I said that when you remove concepts (aka specific colors of crayons) from the list of available topics that can be included in a game (the box of crayons) then the area your game can cover (your pictures color palette) is not as wide as if you still had access to all concepts (a larger color palette)."
"Previously in this thread I have stated that you shouldn't remove the red crayon from the box, because it limits possibilities in storytelling."
And I'll go through with one last analogy as well.
If a pizza parlor chooses to not sell a specific topping, then that's perfectly OK. Ledo's pizza has salami and meatballs as potential toppings, but Pizza Hut doesn't--but Pizza Hut does have sun-dried tomatoes, which Ledo's doesn't. And California Pizza Kitchen has broccoli and avocado, which neither Ledo's or Pizza Hut sell.
Why? Because they are different restaurants selling different types of pizza.
Just like different companies produce different games and different genres of game with different target audiences, and will thus include different topics. And some companies are choosing not to sell slavery as an option for their pizza.