Some players pay for two accounts to have characters on both horde and alliance factions on the same server.
Why us there a paywall to having different faction characters on the same server?
Should allow cross faction character creation if this is an allowed behavior.
World of Warcraft is a commercial offering. It is not free nor do you have any entitlement to play it for free.
Actually, you can play World of Warcraft (Retail) for free on characters up to level 20.
That’s only for PVP servers, btw, but the answer to the question, I suppose, is quite an easy one; That’s how it was during Vanilla. I don’t think it changed until maybe Cata (or possibly late Wrath some time).