It exists due to outcry based around them repeating a story verbatim with some names changed and what nuance there was stripped out. The loyalist story exists for the same reason things like the Alliance calling out Vol'jin exists or the changes to Tyrande's Night Warrior debut. Or most recently the Forsaken text blurb stuff. The outcry was so pronounced that they felt putting in something would reduce the damage. But that the situation for the outcry exists at all shows the tonedeafness of the arrangement.
It is not made because Blizzard amends to the criticism being made. It's done as a frog-boiling exercise because they think that the issue is that people haven't been primed to accept the thing yet and they would given time. Put another way - it's not that no one wants the Forsaken to strive tirelessly protect the living, it's that they just haven't seen how it ties together yet. It's not that people don't want the Night Elves to be told they're in the wrong for wanting something more substantial after a genocide, it's that the particular encounter is badly done. Or it's not that people don't want to do Mists again and further neuter their faction of internal difference, it's that they just haven't caught on to Sylvanas not caring about the Horde yet.
But in all of these regards, the story intent was blisteringly obvious and called months if not years in advance. It's the direction that is inherently bad, even if the delivery was better. Even if they'd used profane rituals to raise Dostoevsky from the dead and hold him at gunpoint to write their material, it'd still be bad because what is being produced runs counter to purpose of the product.
As for gameplay unity still being on the cards. Possibly, but the Horde and Alliance are very strong branding identities and I don't see Blizzard ditching them even if it'd be a good step in the short-term. Especially not skipping out on doing so to build up hype when the expansion is fresh.
@Ardenaso
Them having said races in the first place makes them bad representatives of Lordaeron, since Lordaeron becomes secondary to their identity. They're fixing the Plaguelands because they're nice dudes more so than out of patriotism or connection to the land.
@Saltysquidoon
I'm of two minds on this. If they had gone ahead with gameplay unification I'd see it as being more of a concerted effort, but if they continue not to, as has been signalled thus far, then I'd chalk it up mostly to the writing department being given far too much leeway to moralize without necessarily reflecting on the product they intend to put out. Or in Afrasiabi's case, getting one over on Kosak for denying him this storyline back in Mists in favor of the Garrosh one.