Another thing I am seeing in these thread is the "sameyness" of themes.
It's always
- Kitchen sinks
- LotR clones
- Human centered
- Real World History with countries painted by races
DMs in this thread have been suggesting the same 4 family of ideas over and over.
So, one helpful thing that serves as a "common sense" check is to see if you understand other people's position.
There have been a (relatively) few people that have espoused running a human-centered (usually, human-only) campaign, such as
@zarionofarabel .
But the rest of this is not, in fact, true.
What "DMs in this thread" have been saying is they restrict and add things (races, classes, magic items, backgrounds, and so on) depending on the needs, theme, and fit for the campaign. The primary argument has been between those who assert that it is somehow "unfair" or "wrong" for a DM to do so; that, in effect, a session 0 DM restriction is simply an opportunity for a player to create something not allowed and make the DM "justify" that restriction (which the DM shouldn't be able to do, because restrictions to players are anathema, and any good DM should be able to change their world to fit what the player made regardless of what the player is doing), and those who say that a session 0 DM restriction means that a player who demands to play something outside of that is an entitled and obnoxious player who needs to be booted to the curb, quick, because this is just the first sign of behavior that won't stop any time soon.
...I kid. But that's the kind of calcified and reductive arguments that we are seeing. Usually, people at a table communicate and solve these problems without all ... all of this. These arguments are fundamentally about people's experiences, play-styles, and trust. In effect, one group believes that players should abide by session 0 restrictions set by the DM, and the other group believes that the DM shouldn't have session 0 restrictions. Every thing else is just noise.
Turning to your point regarding races, most of us have stated that we often use "non-standard" or "non-core" or "exotic races" that are themed to a campaign setting. For example, in another thread I mentioned a Yuan-ti campaign I ran a while back. Others, such as
@prabe , have discussed their process for adding non-standard races.
In effect, most of
us (the DMs that you speak of) are saying that there are two types of campaigns ... in fact, many of us run both. Kitchen sinks, in which anything goes ... or, with some type of
de minimis restriction (no UA or homebrew, or PHB + Volo's, or PHB + setting book you are in, or any official material but not Tasha's, etc.).
The other campaign is, for lack of a better word, themed. It has been designed to have a subset and/or superset of races. Perhaps some of the races have been cast aside for mechanical reasons. Or because everyone hates Kender. Or because they are elves. And maybe the DM included "Reptilians" instead of "Lizardfolk." The point being that the world is restricted/changed from the default, something that has been happening for nearly 50 years in this hobby, and that I hope never changes.
