How did monotheism become so popular?
Polytheism described reality in terms of a bunch of specialists. You had a goddess specialized in love and a god who was specialized in war. If you needed help in battle, you call in the war specialists. Monotheism integrated all the specialists under a single principle; God the King of Kings.
This integrating affect allowed the team to become more than the sum of its parts. There is a time for everything since it all under one principle. In polytheism, the gods and goddess were often divided in politics. This was not a good team. But monotheism changed that;
A time to be born, a time to die
A time to plant, a time to reap
A time to kill, a time to heal
A time to laugh, a time to weep, etc.
Relative to the human personality, for the ego to become well rounded and balanced; reflect the inner self, required an integrating principle. It had to do with the layout of the brain's operating system. There is an integrating factor called the inner self. It has a jukebox of apps that are called the archetypes of the collective unconscious. Polytheism was more connected to the individual apps, while monotheism was connected to the underlying principle that ran the entire show.
In polytheism, if you wanted to become a good soldier, you would worship the god Mars. But since the gods were not all friends, or all on the same page, you could get stuck being only a soldier. This was not healthy. With monotheism, since God was over all the apps, you could become a solider and then a lover, since there no conflict in the jukebox playing one or the other; there is a time for all things. This allowed people to become more balanced which allowed persistence in culture, based on this merit of completeness. Today we have a choice or not.