Because they want to play Blood Elves on Alliance side.
They call it the High Elves that are still with Alliance, even though Blood Elves are still the same race as High Elves.
Ion said Blood elves evolved pass blue eyes in a recent interview and now the pro-helf are twisting the words and making it sound like Blood Elves evolved as in genetically.
They will think that Blood Elves drank fel and mutated, they did not. They had their eyes change from being near fel. As did any High Elves not with the Horde who went to Outland. The game doesn’t do a good job at showing how the state of things have changed. Many zones and NPCs are stuck in a time bubble.
They ask for skin tones similar to Blood Elves. I’ve seen them ask for the Blood Elves hair styles. I’ve seen them wanting Paladin on Void Elves.
They are asking for everything and anything that is or could be related to Blood Elves who are the exact same race as High Elves. The only difference is eye color lorewise. That is it.
I see them say “Oh, well, they could have larger bodies from not relying on magic as much” Sounds like a Blood Elf Warrior to me. 
Like I said, anything that is or could be thought up for High Elves should be added to Blood Elves.
New skin colors, eye colors, hair styles, tattoos, scars, etc.
I’ve been playing Blood Elf since Feb 9 2009 and I enjoy the Horde. It’s bad enough Void Elves were added, but I swear if they add anymore to Void elves to make them anything like Blood Elves I’m out of this game for good.
I enjoy this game and I enjoy faction identity. Allied races were as big of a mistake as adding Pandaren. Most Allied races should have just been character customization’s, and I think Blizzard knows this now with how they are adding things like Wildhammer stuff to dwarfs and other Troll races to Darkspear, etc.
You talk about “Don’t ruin Alliances fun by trying to take away High Elves from us”
How about you stop trying to ruin peoples fun who have invested a lot of time into this game and enjoy faction identity. High Elves were never added to Alliance. They are just a scattered bunch of NPCs. We could argue any race could be any faction if we started counting player friendly NPCs. High Elves renamed Blood Elves and the majority that was left after Arthas went to the Horde.
Mr. Ion, I say it’s time you put this topic to an end, because all it’s doing is causing way to many forum threads, fighting and stress. Enough dancing around the questions. Afraid people will quit? I’m about to because we keep not getting answers. Just vague answers that can be taken 50 different ways.