For months, the community has discussed the massive removal of dislikes from the Diablo Immmortal trailer's YouTube page. Content creators or influencers have also highlighted the topic widely.
However, Caden of the House known as Ythisens has come forward to share his personal experience while he was still a community manager.
Ythisens was one of the hundreds of Blizzard employees laid off early February 2019. But now that he is no longer an employee, he decided to come forward by sharing what happened behind-the-scenes.
Blizzard Entertainment was not aware of the reason thousands of dislikes were removed. Blizzard didn't remove them, nor requested YouTube to remove them. As a matter of fact, Blizzard still doesn't know why that behavior happened, as YouTube has not responded Blizzard's inquiries of the matter.
It seems the exorbitant amount of dislikes might have been generated by multiple fake bot accounts that got banned by YouTube. That sounds like a logical assumption. But same as you, Blizzard has no clue why the dislikes started to disappear en mass.
CadenHouse's tweet may be found here.