There are plenty that do. They end up making waves in the libertarian and conspiracy communities and are generally blacklisted by the mainstream press.
The two communities above are receptive to messages about government overreach and corruption, the general public seems not to care much.
I suspect this is largely because libertarians and conspiracy theorists (which do overlap to some extent) are already skeptical of government "goodness" and anything that feeds that skepticism is easily accepted. The general public places government on a higher moral plane of existence and any challenge to that is met with skepticism and excuses.
The end result is that those that speak out/expose the government are sidelined and punished through smears or government action. See: Attacks on Gabbard, Ron Paul, Snowden, Bill Binney, Assange, etc.
It always fascinated me that the discussion of the leaked Clinton emails conveniently focused on the speculative source and motivation, never on the content of the emails with valid DKIM signatures. There is literally no question that those emails are real and unaltered.
