That's because mediocrity breeds mediocrity. Organisational leaders who invest (in quality of learning, culture and people) less in their HR function tend to breed mediocre HRs. Lack of thought process, thought leadership within the organisation and focus leads to failed HR departments. After a certain amount of time, the culture trickles down and becomes incurable (unless someone really strong steps in and take bold decisions). HRs forget that they need to treat everyone as adults.
People who have seen, breathed and lived mediocrity can produce only the same. Good organisations and leaders devise culture and empathy in a totally different manner and hence their organisations have better HR professionals.
BTW, HR here, though without any moral highground :-)