Trying to base world demographics on the composition of adventuring parties is a lost cause, and always will be, in any setting.
And yet, every single D&D setting does EXACTLY that. Oh, look, Greyhawk, Forgotten Realms, Dragonlance, on and on... we have a majority of humans, then elves, then dwarves, then halfings and gnomes. Gee, almost directly pulled from the PHB. Yup, you have the odd "monstrous" states like Pomarj or various parts of Forgotten Realms, but, overall? Pulled straight from the PHB.
Good grief, Candlekeep Mysteries gives me an entire village of frog people but can't give me so much as a farm with dragonborn in it? No one is saying that the base demographics have to follow adventuring parties, but, it would be kinda nice if, upon deciding to play a dragonborn or an Aasimar, you weren't immediately forced to be from "far away parts" because there simply isn't anywhere local for you to be from.
I mean, if I play a halfling in Phandelver, no one so much as bats an eye. Heck, there IS a halfling family in Phandalin. But a dragon born? Naw, you have to be born half a world away.
I agree, we don't need to add in every single race from every single book. But, the PHB? Considering just about every single setting out there is based on the PHB races? Not really a huge ask.