Why going to HR generally doesn't help targets of workplace abuse

Targets of workplace abuse have told me that when they reported their experiences to Human Resources, the workplace abuse generally got worse. Advocates said:

HR is there to protect a company's legal interests, not the worker. As soon as a you go to HR [about workplace abuse], you can expect things to get worse because you have just given them notice they need to get their ducks in a row and get rid of you so you can't document anymore. It's better to quietly go to an employment lawyer who will tell you if you have a case, tell you how to document, and act as your advocate when you have a viable case.

HR gets their paycheck from the company, not you. They are not your advocate.

Going to Human Resources can be as effective as doing nothing, if not worse.

It is important to note that many HR professionals are targets of workplace abuse themselves.

What do you do instead? Advocates most commonly reported that leaving the organization was the most effective (and often the only effective) means of stopping the abuse.