Why do you assume the player hasn’t done any work though?
“Hey, I have a cool idea for a race”, shouldn’t be met with a curt refusal. Once again, D&D is a social game.
I did not assume they didn't. I asked for a courteous level of normalcy. "In an average game, a player, even one that has done the work, has not done as much as a DM that has
put in the work." I would go so far to say this is true for even DMs that haven't done the work, but I have supervised too many high school D&D clubs to know sometimes the DM knows less about what is going on than the players.
And I don't know how else to explain it to you. A DM that hasn't done the work should
accommodate the new race. But one that has done the work, for either their players, themselves, or both; for logic or story underpinning or both; for consistency and future involvement, or for any singular one of those things, doesn't need to accommodate. In fact, it is the player who is breaking a social contract. Can the player suggest it? Yes. Can they sit down with the DM and explain the how, why, where, and when. Yes. And the DM should listen. But, if it derails any of the above reasons, the player shouldn't care if the DM says no. If they have done that much work, they too can start worldbuilding, and then DM the next campaign.
I should note, this is one reason why my campaigns are short. People like to DM. So this gives everyone a chance. It also allows for the story to progress rather than stagnate into an entire session where the group is haggling over the price of a ferry to cross a river. But again, I like creative constraints.
Stubborn people are stubborn. I cited my principles for DMs upthread, but they also apply to players:
1. If something doesn’t work explain why;
2. Be open-minded;
3. Try to come to an agreement like a reasonable adult.
I agree with all these. Especially be a reasonable adult. Any reasonable adult I know doesn't insist
on altering someone else's hard work. They find a way to appreciate the work for what it is, and if it is not for them, they themselves can create a work.
I don’t think it’s strange: it’s related. A player already has to deal with many limitations, why are you adding more?
Conversely, a GM has exceeding few limitations: they can if they want to (but aren’t required to) create a whole world.
I would strongly disagree with the above bolded statement. Perhaps, that is where we actually disagree. A DM is awash in limitations, limitations that are much greater than a player's. Please allow me the opportunity to explain.
As has been mentioned, this is a social game, and the DM is trying to fulfill the needs of many players, not one. That constraint limits any caring DM greatly. The DM must also hold bear to outside pressure - players wanting to use all books (sometimes even 3rd party books). This may not seem like a pressure, but it is pressure: by the publishers, by the players, by outside groups, to conform. One only needs to look at the racial attribute bonuses to see an example. Then there are all the regular constraints that the players need to follow. I mean, I don't know of any DM that cares about the game, that would give their first level antagonist a +15 to hide. I don't know any DM that cares about their D&D world that allows a creature that was presented in the lore to suddenly be completely different. Which is the last part - a DM that cares is beholden to their lore. Their creations. Which is a far greater constraint than any player ever has to deal with. One just needs to look at a DM world that has extremely limited magic. It rarely means the player can't be a wizard. But it does mean that every goblin group the party comes across doesn't have a shaman.