St. George Decoded - Converting the Opposition, page 12
To our minds today, this business of dragons/Draco, knights/Perseus, princess/Virgo all seems to be somewhat abstruse. To our ancestors at that time, the sky was the domain of gods and what happened up there had significant effect down here. This is the milieu into which the Christian Church was born, so it is hardly surprising that they should lay claim to a unique precessional event and encode it in time-honoured fashion by way of mythology. It must have been too good an opportunity for the early Church to miss when the rival cult of Mithras had claimed an exclusive prerogative in these precessional events.
For some time there must have been conversions to Christianity by former followers of Mithras. In the battle for hearts, minds, and souls, recent converts from Mithraism must have known how to dress up Christian stories in Mithraic terms to attract their former fellow cultists. They could show that while it took the full godhead Mithras/Perseus to do the precessional deed, the Christian God was so much more powerful that He could assign a knight to do the job instead.
Our story here is about St. George only, but in a broader context, the early Church effectively laid claim to the whole system of equinoxes and solstices. In summary:
Once the Christian Church prevailed, and Mithraism (and other sky cults) had withered, the precessional interpretation of St. George, the Princess, and the Dragon was redundant. St. George could now be dressed up as the first hero of the age of chivalry, his shining Christian persona an example both to individuals and nations alike.