Bingo!
"Mandatory Reporting" laws have been in existence for many, many years. All health care providers, not just MD's, are required by law to attend periodic training to educate them on what to look for and how to intervene - the training is mandated by the government but must be paid for by the provider's employer. This includes dependent adult abuse reporting as well as cases of suspected child abuse.
So, not only does the government require reporting of suspected abuse, but private institutions are required to foot the bill for the education requirements.
"...doctors should not have to report suspected cases of domestic violence or child abuse either"
That is a completely different situation, apples and oranges. I'm not sure I agree with mandatory reporting, but, in the case of domestic violence the patient is presumbably the victim of a crime that will otherwise go unreported, because the victim/patient won't report it. It seems that this proposed law would force doctors to report their patients as presumed criminals, regardless of their ailments.
A closer comparison would be to a situation where a person comes in with injuries that might have been sustained during the commission of a crime, like a gun shot wound delivered by a shop owner, etc. resisting a burgaler. Are there any mandatory reporting laws for these situations?
The difference is that when you report an abuse case, someone does something about it.