Yeah and that's the problem.
Have you seen how the lore of elves is basically nothing? That's because they aren't allowed to have a culture because every setting has a unique culture for them that doesn't mesh with any other. If D&D had one setting (let's just use Greyhawk as the example) you could talk about elves coming from common homeland, having a common culture and unique traditions that elves from that land share. And then you can have elves that don't fit the norm or come from other places play as exceptions via customizable cultures. But the PHB elf has to fill the role of the Tolkien like elves of Oerth, the slightly different ones of Faerun, the radically different ones of Eberron and Athas, etc. So you get the most generic, bare bones stuff because it has to support a dozen different worlds.
Maybe a better example. Xanathar's Guide had a samurai subclass. How many D&D worlds is samurai actually a thing? Faerun has Kara-Tur. But is there an Asian feudal society on Oerth? Krynn? Eberron? Athas? Not to my knowledge. It's a player option without a home in most official settings, requiring the DM to refluff to something else, add lore content to justify, or ban for not fitting. IMHO, a official D&D option should work with an official D&D setting without the DM having to justify why. That's why I bought a setting rather than homebrew, to have that done for me. But with so many settings having narrow niches, it fails despite the samurai being an option for the game since 1e.
And if samurai is too niche, how many official D&D settings ban orcs? Too many IMHO.
One setting. Like Golarion, has a place for everything in the game. You wanna homebrew? Pick and choose. But the default game should accept all parts of the game without bans and work arounds.
And I say this as someone who deeply loves Eberron and Ravenloft. But I know it's better for the game to have one catch all setting than a patchwork of settings that are only vaguely compatible.