Whyever not? They’re spending a lot of time and energy telling us that we’re bad people and have joined the bad faction in this expansion.
I don’t know how long you’ve been reading the boards, but it was confirmed that there are two story teams for at least the leveling content in BfA. The san’layn and Brennadam storylines were written by the Alliance writing team for Alliance players. We can only speculate as to why the Horde writing team didn’t also use them. But given the tone of the rest of the expansion, I don’t think it was out of a desire to make the Horde look better to the Horde player. (See thread below for more on this.)