The world’s great religions are particularly monotheistic. The idea of monotheism originated in the India/Middle East area and spread. Prior to that there was no particular push to swap out your pantheon of gods with anyone else’s. The viking pantheon was pretty similar to the Roman which was pretty similar to the Egyptian.
Monotheism was new and interesting and tended to proselytize more.
Perhaps (and I don’t know) monotheism developed in other places and didn’t spread all that much, but the India/Middle East area had the advantage of being the middle of the world as well, sitting on the center of the silk road and having the vast Empire of Rome on one side and the vast Empire of China on the other.