Maybe they realized that if every post is "Happy, Happy, Joy, Joy", people will get suspicious that negative posts are being suppressed. Whereas if they let a few, carefully selected, mildly negative posts through, people won't realize that all strongly negative posts are being suppressed.
And who knows, they might even let a strongly negative post through once in a while (as long as it doesn't mention their violation of their own legal agreements or other such "sensitive" topics), just to help keep the wool firmly over people's eyes.