I've had coworkers who put other coworkers first.

Ive never seen or heard of an HR department that didn't put the dictates of management first.

You're comparing individuals to departments. There are certainly people in HR who have put coworkers first. Depending on the company they may have succeeded or not in those actions. "The dictates of management" are what departments do.

I've had co-workers who I considered friends but was disabused of that thought once they no longer needed me for something.

Workplaces are funny environments, they aren't natural places to be.

So true. More often than not, they see you as an obstacle.

Speak for yourself please. Respectfully, this level of cynicism is not shared by everybody.