Because, existing or not, all religious references are indeed invisible and therefore useless — if the flag is meant to inspire people and not only the scholastic investigations of various experts.
What was then the true symbolism in the flag, the one that made the specific design acceptable? It is reproduced even now in the official pages of the European Union. This flag is adopted as an image of unity and perfection.
And of course under the number 12 one can put whatever at will, from the signs of the Zodiac to the apostles and the months of the year. And so, if Europe becomes Christian, it will be very well celebrating the flag as a reflection of the Apocalypse, if it becomes Muslim, it will be celebrating the relevant notions, and so on, and if it won’t become anything else but a cohabitation of irrelevant peoples and cultures, this constellation will be equally able to express it with just its vagueness.
Vagueness is the main definition of a culture without culture, and a symbol more vague than this flag and suitable for the New Age is difficult to be found. This is the reality concerning the nature and aspiration of the European flag, and not an honor to Virgin Mary or any other reference to Christianity.