Even where it exists, doctors have to weigh whether the abuse they receive is worse than they'll receive after going through CPS and foster system. Anecdotally I've heard from medical providers they prefer not to actually report unless the kid is literally imminently going to die, because the foster system is often even worse for these kids.

I find that very hard to believe, because the law doesn't allow it and the penalties for noncompliance with mandatory reporting are severe. In many states, failure to report is a crime. Mandatory reporting is intended to remove that kind of subjective evaluation from the picture.

OK, fine, don't believe it. I'm not here to convince you how it's nigh impossible to prove what a person is thinking at a particular time. Mandatory reporting is basically a thought crime, if you have the wrong thought (thinking someone is abused), you go to jail for having that thought and not telling someone. Thought crimes are basically impossible to prove in anything other than a kangaroo court.

The real risk is civil liability. Particularly if the victim is later injured

Hmm, fair point.