In essence, HR is the buffer between humans and systems. They create the systems that allow humans to do things like work and be compensated for their work, or to work in an environment where they can expect not to be harassed—at baseline. They clean up everyone's mess when the interface between human and system is compromised.

If a system breaks down, it's HR's job to figure out how to handle the errors. Every company's HR will encounter unwinnable situations where all HR can do is remember the "error code" for next time and, if they're lucky, create systems or policies that prevent it from happening again.

Some (very few) companies have more thoughtfully designed systems that enable the HR team to act proactively on behalf of the employees.

And some (most) companies are poorly structured such that the system is constantly breaking and it's HR's job to keep the company's cadence going as best they can.

I'm guessing most people in this thread have experienced more of the latter.