Blood Elves stopped being Alliance after the 2nd War.
It clearly states that Anasterian did not feel that the Alliance had his people's interests at heart and then we had Garithos afterwards.
The Blood Elves and Lor'themar especially, had a clear link with Sylvanas, which in turn, brought them closer to the Horde. Kael'thas was aware of this allegiance and he pushed for it through Rommath.
Lor'themar had no links to the Alliance, so joining the Horde was (and still remains) the better option.
If they were alliance, they'd be enveloped into "Human Potential" and we see how well that works for the Night Elves. It's part of the reason why I am such a Blood Elf fan - they would have 0 charm being Alliance. So bland and boring and just LOTR - I mean, if you want to play a race, that is allied to Humans and looks like Blood Elves (without the void stuff), play LOTRO.
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Well, it's not about letting the elf haters get to me, it's all about what's fair. I mean, elves have 4 playable races at the moment. We're not exactly bleeding for options.
And, I remember how I felt when I saw WoD for the first time:
"Great...more Orcs!"
I don't want that same feeling to happen, about Elves. Yes, Elves will take a big stage in WoW because they are a large species, but just like Orcs in 2014, you can have far too much of a good thing.
I'd love more Blood Elf options, but I'm a realist and the fact is, we aren't starved for options. We can play as 4 different elves and RP 5 different elves. Sometimes, we have to take a step back and let the other races have their time. I mean, we're all still waiting for the Draenei and Darkspear Heritage armors.
Maybe San'layn/Dark Ranger options come available in 11.0 or something? Maybe "Rommath/Magister" tattoos come then as well?