Even today different German agencies or public institutions are not linked. If you marry, or get driver's license, you have to fill all kinds of forms, maybe get a birth certificate etc, because they can't just ask a different office to give it to them.

As you said, this is so nobody in government can collect all kinds of data about citizens, to do bad things to them.

Some people would like to have, say, a public wealth register today, and the above is exactly why others heavily oppose those ideas.