Y'know, something interesting I've seen brought up by developers in the context of new editions of games is the issue of bringing old content forward. The discussion was about updating the World of Darkness games into new editions and the devs were discussing how with new editions, often people expect stuff from the older editions to immediately be brought forward into the new edition on top of new stuff for the edition. So when I think about it in those terms, it does make sense to me that D&D gets more unusual races added onto it as core races as time goes on. You still have humans and dwarves and elves, everyone is familiar with that, but people want new stuff and designers generally like making new stuff. So why wouldn't you get more new races and potentialy new classes in the next edition of the corebook?
I wonder if part of the issue isn't that the D&D corebooks seem to try and be pseudo-setting agnostic? Like, you get setting information from the writeups of races and classes, but the books don't give you an actual concrete setting with nations and plot hooks and things. As someone for whom D&D wasn't their first rpg, it's actually kind of weird to me. There's definitely an assumed default setting, but it's not truly stated. That lack of stated setting means that from a story perspective, there isn't really any limitation on what they can or should include or not include in the core book. In a way it's almost better if the corebook introduces a wide variety of races to suit anyone's playstyle. If people want to make a low fantasy setting, they can do that. If they want a high fantasy setting with a lot of weirdness, that should be supported as well.
