Belf is a very separate thing for three reasons. One, it's the only non-monster looking horde race. So, yes, people who wanted to stay horde but wanted to look like a human did go over there, but you're talking about the casual crowd. Two, their racials were insane when they released and completely shit on draenei's heal/hit. The aoe interrupt was monstrous during mace stun and fear spam days. Three, paladins were needed on horde side because it was the only tank class being held behind faction lines. Once they reworked totems in TBC shaman wasn't really something alliance needed.
Just saw your edit, not sure why I can't bring waifus into if you only play waifus. So make a waifu.
