Two possible explanations:

1) the site editors are sincere independent media types, but they are not properly educated in the ethics of journalism and democratic political theory, and they therefore are fanatical enforcers of their own personal blend of media activism. Some indymedia workers think all allegations that the US government and the US military and intelligence services commits evil deeds are "conspiracy theories". In addition, if there is even one political Zionist on board an Indymedia editorial committee, then they will usually find a way to censor all direct criticism of the Israeli government, worldwide Zionism, or the Washington neocons.

2) The CIA, NSA, etc. has infiltrated and now controls many regional Indymedias.

3) As the primary editor of one Indymedia for three years, I am certain that the first explanation is true for many Indymedias. I suspect that the second explanation plays an increasing role in many indymedias.

Independent media activists and volunteers are often well meaning, but they are often also ignorant of human rights, civil liberties, journalistic ethics, etc. They abuse their power to impose their own personal narrow view of the world onto the Indymedia community.