We're also past the 20 year mark where higher ups and those potentially in the know are retired and at an age where they're losing their health and influence.

I work for the government. When I see someone from 20 years ago fucked my reaction is "someone from 20 years ago fucked up" and the old person in the office goes "oh yeah they retired a few years after I started" and you move on and fix the fuck up, not cover it up to protect someone who has been retired for 17 years from a 17 year late negative performance rating.

Obviously a 911 conspiracy is more significant than someone who wrote an incorrect report or whatever but the fact is that the government is millions of individuals and you need a whole lot of loyalty to keep secrets safe once you're gone, same as any large organization.