Without knowing any detail my suspicion is the usual one of the "old guard" in engineering, who fully understood how to be good engineers and the importance of HUMS, booted out / retired / retired early due to getting burnt out, and replaced with cheaper inexperienced newbies who don't have quite the same ethos or ability to stand up to ignorant management. Speculation, I'll admit. But...
Probably not so far off base as One might think.
Washing out experience is a pitfall of modern management practices sometimes.
For sure what does happen is a "loss of corporate history" when long serving skilled and experienced Staff leave and the new are presented with a great opportunity to repeat history they know nothing about.