I think that Einstein's Jewishness is a significant part of his notability. His parents were Jewish. He strongly identified with being a Jew throughout his adult life. He is mainly famous for being a physicist, but he is also frequently quoted for his opinions on God, religion, and peace. He was an active Zionist and a Nazi refugee. He is especially popular among Jews. As another editor says:
He described his 1923 visit to Palestine, where he was mobbed by Jewish throngs as "the greatest day of my life". He was on the first Board of Governors of Hebrew University of Jerusalem.He left his assets to Hebrew U. People are fascinated with the details of Einstein's life, and his Jewishness is one of the first things they learn. Saying he was Jewish is as important as saying that he was German-born.
The strongest counter-argument is that the Martin Luther King, Jr. page does not say that he was black. I think that is a little strange. My guess is that King's fans are trying to make some sort of point by ignoring the color of his skin, since King was famous for opposing racial discrimination. But I am not sure what the point would be to ignoring Einstein's Jewishness.