@Awoo @lina yes, they changed it years later, but back them race/class combinations were pretty restrictive. Heck, IIRC, Trolls and Gnomes had only like, 4 classes available to pick in vanilla. And also back them the Horde and the Alliance were completely separated, they could only fight each other, no way to do raids together.
This actually helped a lot to make the factions and races distinct from each other, but I bet players (or at least a vocal subsection of the players) complained that it "hindered their ability to be creative" or some bullshit like that, and then Blizzard started changing it.