Shareholders. The people Activision make their games for.
Good, this is people with some influence saying “we don’t trust you to investigate yourselves and then say everything is okay. Nothing wrong happened here.”
It's likely more a motivation of trying to force them to stop generating bad press and hurting profits more than shareholders trying to actually make the company a better place on a moral front. Majority share holders in Activision Blizzard are just other institutions, not your average consumer.
Are shareholders villains?
There's literally no conceivable justification you could give to vote against that level of transparency unless you intended for the abuse and discrimination to continue. The fact that the board of directors recommended voting against it means that the purge of abusers has not yet gone far enough.
Shame most of them are only concerned about future skeletons falling out of the closet and putting a dent in the stock prices.