I used to think this when I was 16-20 playing in wrath and cata (in tbc I was too young to care, literally only played male characters and had fun), and I can explain it. At one point literally every character I had was a female human/belf.
The reasoning is that they generally look goofy and stupid, and the consensus is that the people who play them are casual or mediocre players. I mean, normally when you see someone post some dumb thread on general discussion, it’s going to be a male human/nelf/draenei showing an untransmogged helmet and cloak. Generally female characters in games look better than males anyway, and that’s what it boils down to - making your character look better than everyone elses, or at least stand out.
However, I grew out of that phase around MoP and realized that no one gives a damn what race/gender you play in reality. In fact, the race combos that garner the most attention are the ones that are the rarest.
Dunno how many downy kids whine at me for posting on a male tauren all the time