Why do we keep hearing this Horus nonsense?

If you're referring to the fact that most, if not all, of the elements of the Jesus story have been attributed to other god-men who were variously born of a virgin, had a king seek their deaths as a child, born on Dec. 25, etc, hey, that's the way it is. Most of the elements of the Jesus story have their origins in older stories. Religious beliefs shape the form of the myths of the god-men, not the other way around.