There are a few reasons, but one is that well-connected rich and powerful people and their lobbyists can get all of these people on the phone. The "private" pressure is constant and always leans in the direction of elite impunity.
Who do you think all these powerful people hear from regularly? It isn't people saying it is good to hold other powerful people accountable!
I mean, if you indict one member of Congress for sex trafficking, where will it end? Slippery slope! Some of our faves might be implicated!