And, whiff, there goes the point off over the horizon again.
It's not the only way. Good grief. Of course not.
But, if I choose to play a human or an elf or a drow or a dwarf or a gnome or any other PHB race, I can connect to an existing, canon NPC in the setting IF I SO CHOOSE. There is no "must" or "only" or "need". It's that the OPTION EXISTS while it DOES NOT EXIST FOR SOME RACES.
In a setting built based on the current PHB, then ALL PLAYERS WOULD HAVE AN OPTION REGARDLESS OF WHAT SPECIES THEY CHOOSE!!!!!! As it stands now, because these settings are so old and based on editions long out of print, NOT ALL PLAYERS HAVE THE SAME OPTIONS.
Is that clear enough? Yes, you can adapt. Yes you can create. Yes you can do all sorts of things. BUT YOU CANNOT LEVERAGE LORE THAT DOES NOT EXIST.
Why is this so difficult to understand?