I play Horde, and I cannot play Alliance, even if High elves were available, I simply don't like the faction.
However, I have been playing Blood elves since I started playing a decade ago and even I can understand and see why High elves make sense.
It's so simple, the WoW team has placed High elves in the Alliance, and thus, they are also part of the overall Alliance fantasy, and from my perspective as a Blood elf player, I cannot but see cool things on it.
They are also Quel'thalas fantasy, just not the one that Blood elves (on the Horde) provide, the matter of them being on Alliance is not detrimental to the Blood elves, but an addition to the overall theme of what they are and what happened with them. Not everyone stayed in Silvermoon and there are some who go against the current status of the realm and fight against it from the Alliance, it's a completionist goal for the lore of the game.
Seriously, one can ridicule it all he wants, but at the end of the day it's simple as that, High elves exist in the Alliance, so people ask to play as them.
Not LoTR, not ESO, not whatever, it is Warcraft what is being pointed out when asking for the option, because it is something that already exist in Warcraft, and if someone has a problem with it, it's the developers who should be called out on it, not other players who ask for the High elves from the Alliance to become playable.