That's always kind of been the allure of autocracies/monarchy. Nepotism is more or less unavoidable so why not streamline it, while at the same time creating an inherently direct and swift deciding government. 

Of course, there are semi-absolute monarchies like the Polish-Lithuanian commonwealth, the Holy Roman Empire, the Late German Empire, or even Rome where there were two autocrats, one elected and one hereditary. These semi-avsolute monarchs had much power but not all. 

Dynastic power is one of the key points of monarchy, without dynasty you get... lite-fascism I guess. There is also the "mandate," typically of heaven. In my two favorite examples, the Russian Tsar and the combined position of Grand-Duke of Lithuania/King of Poland, there was the mandate of God, particularly for the Tsar Autocrat who was also of the highest religious role. Plus, mandate of the peoples came as Neo-Slavism came to popularity and Catholics as well as Protestants in Poland, Czechia, Slovakia and other lands looked to him as a leader to be.