It's interesting that no advertisers had even a hint of concern when informed about the massive privacy invasions, many of them highly illegal, that Facebook performed for a profit.
That, or they are realizing they aren't getting a good ROI on facebook ads and figure now is a good time to pull out.
This is why some companies worry so much about their ads appearing next to objectionable content. They're not trying to get you to go buy something: they're trying to get you to associate their brand with a certain lifestyle and identity.
If the context changes so those associations become negative, the value of that advertising can swing rapidly.
The fact that some people and some companies get upset about some things some of the time is actually a massive improvement over how it was in the 90's and earlier. A sea change.