We all understand that the story is totally incoherent.
To go with the latest cinematics, take for example Sylvanas working for Kel' Thuzad's and Arthas' boss. Total absurdity.
Now many in the community come up with this reason: "well she did the genocide it because she thought Zovaal would set us all free".
The thing is, that is total headcanon.
For all we know, in game, from Zovaal's quotes and his history from the get go, is that he is totally evil ("mustache curling villain", as described).. he is evil in a cartoon-villain way, totally one-sided.
I.e. let me ask you a question, from your perspective, from what you've seen and know IN-GAME about Zovaal, did it shock you that at the the end of the he said "All shall serve me"? You can answer that on the poll.
Personally, I found it totally normal, because that is exactly what this guy has always been about. Hell, to advance his goals he (indirectly) mind-controlled Sylvanas herself via Arthas, as well as countless/millions others (in Maw and outside).
Therefore, how is Sylvanas "shocked", where she supposedly knew at least had our knowledge in respect of Zovaal, plus more.
The only reasonable (out of universe, breaking the 4th wall) explanation for Sylvanas' actions (and for all other characters' actions) is the following and it's clear as day:
The current lore team at Blizzard (Danuser and co.) is trying to quickly close the established Warcraft lore "chapter" (from WC3), so they can introduce their own new Characters/Lore etc.
To pursue that goal, they swiftly (in basically 1,2 patches) introduced totally new characters with no build-up, made them responsible for manipulating the whole story since before WC3 (so as to prop THEIR NEW CHARACTERS and DIMINISH the ALREADY ESTABLISHED characters from PREVIOUS LORE WRITERS)...
so they "could make the story their own".
In that process, and because it was done so quickly, A TON, literally HUNDREDS of MAJOR INCONSISTENCIES have emerged.
Do you think that the current lore writers had the right to do that, i.e. to rewrite in 1 patch the whole lore just to advance their own new characters in favour of the ones established by previous writers, so they could make the story "their own"?
Personally, I think that is way too egotistical. And it actually shows on how many people dislike/quit because of it.