Twitter’s content was a cesspool and has been for years. I’m not sure what additional harm these brands are worried about.
I don’t think there’s a difference between “we say we’re trying and are completely incompetent” and whatever Twitter is doing now.
This way, if nothing happens, they can always come back silently (or spinning the story in a way they want). If some PR disaster happens, they are safely away from it.
For me, this was to be expected and is a testament of how important Twitter has become in the marketing world that it isn't bleeding out advertisers even quicker.