Why was Imam Malik called "Imam of Imams" and "Scholar of Dar al-Hijrah"?

Imam Malik was titled "Imam of Imams" due to the large number of those who learned from him, either directly or indirectly. He was also titled "Imam of Dar al-Hijra" (Imam of the Abode of Migration) because he remained the sole reference for the people of Medina, to the extent that it was said: "No one gives a fatwa while Malik is in Medina."