I feel that you're answering a bit of a straw man argument.
The topic wasn't how much of their time they spend talking about politics, it's what kind of opinions they express when they do choose to make some public statement related to politics. And the answer to that is that they know who butters their bread (Hollywood Producers) and whenever they say something political, more often than not it's not going to be something that causes them problem for their employment.
Most big actors understand that the more they talk politics, the less bankable they are, and the dollar wins out most of the time.