it might be a liability thing partially, If your compny received published Sell recommendations the stock might tank farther than it would than if a Hold recommendation is given. I can think of at least one example I read about a lawsuit in the news that had shareholders taking the company to court due to a large drop. almost 50%, so if it was found that it could be linked to a news source I'm sure they would be taken to court as well...
Also people don't like to hear bad news, they want to hear the stocks they picked are winners, even if they aren't...