Maybe a few reasons.
Soldiers have to praise the system. It's the law.
Second, the military lives in protected enclaves, travels in at least HumVees, and because they are armed to the hilt have their asses kissed by most folks.
Third, the military is subjected to incessant information (propaganda) from the DoD.
Fourth, there is pressure. No promotions if critical.
And fifth, no one knows how many of those blogs are written by the Dod. One knows that a lot are, but how many can't be told for sure.
Given that, I'd say that one critical post would be equal to about 25 of the Chernofsomeone blogs.
Arf