I'm still not getting it. The argument seems to be "people expect D&D to have elves". Fine. So if I say, "my campaign of D&D doesn't have evles", then you know not to expect elves. Just like you know not to expect elves in Call of Cthulhu.
Hold up. I can't speak for anyone else, but you've skipped a step here. You've moved straight from "my campaign doesn't have elves" to "everyone is officially in the game and someone just brought me a character sheet that says 'elf' and is getting pissy about not being able to use it." The skipped step is a player asking, "Well, why
aren't there elves? Isn't that, like, a central D&D thing? I know I've seen people call it 'pretend elf-games' or something like that before. And the LOTR movies were what got me into D&D in the first place!"
Perhaps it would help if I lay out what I see as the process of play (for "live" friend/associate groups, rather than purely at-FLGS/online play).
1. DM gets an idea for a campaign, or just feels like running something.
2. DM asks people she knows if they have time and interest in playing D&D, maybe gives a SUPER short blurb.
3. Once she finds enough players, DM actually pitches the campaign properly, all the bells and whistles.
4. Players think about it and, ideally, sign up.
5. Early discussions lead into Session 0 (possibly more than one such session) where wrinkles get worked out and character ideas are finalized
6. Session 1, campaign begins.
It seems to me that you're leaping straight from point 2 (or
maybe point 3) to point 6 and treating the remaining points as an instantaneous assumption, which strikes me as strange. There's going to be some delay, some thinking time, simply because people need to decide if they do in fact want to join or not. During that interim period is when a player should ask things like "where are the elves," if that's a thing they care about.
What else is there to say? The DM should allow elves even if they don't want to? Why?
Being respectful to your friends/associates, more or less. You talk it out. You aren't "required" to do it any more than you're "required" to DM. Instead, I see it as a common courtesy thing. Players show courtesy to their DM by not raising a huge fuss about things (even when there's been a clearly bad call or the like), giving more than lip-service buy-in to the campaign premise, and engaging with the game to the DM's desired level of seriousness (e.g. some games are silly, some srs bidniz, some vacillate, etc.) DMs show their players courtesy by listening to their input and constructive criticism, supporting earnest enthusiasm to the best of their ability, and giving fair hearing when a potential conflict arises. Now, listening, supporting, and giving fair hearings don't strictly require you to do...anything. But I think we can agree that
saying you do those things and then never actually
acting on them in any capacity is disingenuous. A DM who claims to listen to player criticism and then
consistently continues to do what they were going to do anyway...isn't actually listening to criticism. That's where the "required" comes in; it's not that you have to budge on
any given thing, but that for things like "compromise" and "respect" to actually exist, you really do have to GIVE some of the time.
So: Is it an absolute, bright-line unavoidable OBLIGATION to allow elves? No. But allowing them
unless you have good reason not to--and no, I don't accept "because I just don't want to" as a reason!--is one way, among many, to demonstrate that you actually DO listen to your players. That you recognize that while the game is
run by the DM, it is
run for the players. That both parts of that equation are vital, and that you actually do
respect them as opposed to simply
ruling over them.
As for why elves
in particular get this attention? Well, two reasons. Tolkien looms large over the D&D space forever, because he was THE Bad Donkey worldbuilder. And because elves are listed in the core book, which (as I argued much earlier in the thread) is a perfectly valid reason for a
player to assume the option is implicitly offered, and to ask for ways to incorporate it (or a substitute) if the DM has excluded it. Doesn't mean it WILL happen. But "oh, this...is D&D, I thought that meant elves?" is NOT some wacko irrational demanding thought. It's strongly implied by the game's history, the current context of gaming, and the existence of player-accessible material. Hell, you can even argue that the PHB backs me up on this with that codswallop about "scattered among these races are the true exotics," or how "Dwarves, elves, halflings, and humans are the most common races to produce the sort of adventurers who make up typical parties."
They are a core race, you are into houserule territory there. You could do it but I would expect less player interest for that one. If you had a tier list of popular races I guess elves would be up there. I wouldn't argue with you if you said no elves though.
Elves are consistently the second-most-popular race in 5e after Humans, according to data collected from D&D Beyond. Humans are always just above 20%, elves are around 13%, and half-elves are just a hair below that. The next three races are usually dragonborn, dwarf, and tiefling in varying order; as of the most recent shared numbers I could find (from 2019), tiefling is #4 and dragonborn #5, each slightly under 10% of "active" characters on D&D Beyond IIRC.
So yeah, when almost as many characters are elves or half-elves as
humans, at least from what limited data we have? You're probably gonna have issues if you exclude them from the game. Odds are
extremely good SOMEONE in the party is going to want to play SOME kind of elf-related being.