Remember this accident involves a US Army Black Hawk helicopter and the Aircraft Spec is derived from US Army Specifications not the FAA or NTSB.
Also, the NTSB can suggest only and it is up to the FAA to require such devices.
The NTSB has made many such "suggestion" that the FAA has refused/failed to implement.
Also as Wrench rightly points out there are legitimate issues that have been a hinderance.
It is not just the Operators that are the problem.