I don't understand that last bit : in my understanding, the way that social security numbers are used in the US would be illegal in most (?) countries in Europe

I don't understand that last bit : in my understanding, the way that social security numbers are used in the US would be illegal in most (?) countries in Europe ? For instance, in France specifically since the 1974 SAFARI scandal that resulted in the creation of the French data protection authority and assorted laws in 1978, and happened when the government in secret attempted to (and had to stop due to the outrage) link various (then paper) administrative files into a centralized computer database through a single social security number.