Well, in the rest of the government, particularly in the intelligence community, the IG is not one person but a staff, and they can’t stonewall since complaints are a matter of record, reviewed by multiple people. The IG in these cases have no vested interest in stonewalling any complaints because their charter is to investigate and make findings. They aren’t under the command of any single group and they can’t be pressured by people who have no impact on their careers.
That is true in the Air Force, as well. There is THE IG, at a particular base, and they have a staff. Then there is the Command IG, as well, and the Air Force IG. People who are old-timers know to go around if necessary, but some folks don't know that. Looks like the guy in this article was one of them.
There is also pressure to address issues at the lowest level. Sometimes that is a good idea, and sometimes not. Especially when the lowest level IS the problem.