Sin’dorei / Quel’dorei is now a political schema; while they are the same race, there are two sects which have vastly different political ideologies and allegiances.
It should be no different than Kul Tirans / Gilneans / Stormwind Humans / Lordaeron Humans - but Blizz got bold and said “we need a new human model.”
It is frustrating, to be sure, that Blizzard keeps saying we’ll never get high elves, and that there are too few to be a valid racial option… and then they start throwing high elf npcs into every facet of the game just to rub it in players’ faces.