Probably because Monotheism started with the predesessors of all 3 you mentioned.
Monotheism actually started with Judaism, but since the Jews kept to themselves they really did not evangelize. Joining the Jewish tradition was also very off putting since you had to slice off part of your manhood, and you were not allowed to eat perfectly good food.
Christianity basically tore "Paganism" to pieces. It obliterated the long standing customs in about 300 years or so. Do you want to know why? Even before Constantine and Theodosius I, Christianity was spreading like wild fire. There is quite a bit that can be said historically, but lets just say that Christianity was very appealing to the pagans since it was designed to identify with pagan ideals.
Couple that with fear of eternal punishment, and the "he said she said they said" miracle accounts, and voila, you've got yourself the recipe for world domination.
Many of the converts were the uneducated and of the gullible kind, which make up the majority in society. This led the empire to make some decisions for the sake of not losing grip of the people since Politics and Religion went hand in hand in those days. (Not sure which came first though)
Fast forward almost 400 years, and Rome has made Christianity the official state religion. Protestants somehow think that they are the originally intended "correct" version of Christianity, when in reality there would not even be a Christianity if it wasn't for all of the stories peddled by the wealthy Roman elite.