A lot of the reason HR departments behave the way they do, is because of who they report to. The people in the C-suite set the tone and if they create a culture of sweeping things under the rug or otherwise excusing bad behavior, HR will do that too.
The other thing is that people bring their bias with them and an organization's culture can make it worse. If someone is a bit biased against victims of harassment, in HR they'll tend to side with the harasser. If the culture of the company already tends towards hostile/indifferent/unsupportive, it only makes HR's behavior worse.
The other thing is that people bring their bias with them and an organization's culture can make it worse. If someone is a bit biased against victims of harassment, in HR they'll tend to side with the harasser. If the culture of the company already tends towards hostile/indifferent/unsupportive, it only makes HR's behavior worse.