That would be for example considered in Germany a huge breach of the citizens privacy. Simply unimaginable if you were raised in a country like Germany or US and i certainly support this to be private data.
What benefits? If i dont want this data to be public that is my decision which should be respected. I am glad that this is also the stance of my government.
Harder to hide tax avoidance if everyone knows the ballpark of what you make. If you buy a new car each year but pay nothing in taxes, it's immediately obvious.
It can help lessen pay gaps. Between genders or other groups. Removes the power from the employers when you know what you should make.
Makes it easy to see if someone is making loads of money while underpaying their employees.