Why is not Albert Einstein called a PhD?

I am sure that while in Europe, he was called either Dr. Einstein or later Prof. Einstein. Even in the US, he was called at least Dr. Einstein. See examples below. read more

Albert Einstein was awarded a PhD (Albert Einstein - Wikipedia), and is widely referred to as a PhD. But he’s not called “Albert Einstein, PhD” any more than we write about “Marie Curie, PhD”. read more

Einstein was awarded a PhD by the University of Zurich. I'm sure some people in those days referred to him as Dr. Einstein. The fact is, Einstein learned what interested him, loved learning, loved challenging, and didn't give a tinker's damn about a piece of paper. read more