Are not the candles supposed to be 100% bees wax as instructed by the Blessed Mother? This is the case not because beeswax has some mechanical or magical power, but simply because those are her instructions for whatever reason, and we are to be obedient to her instructions so the candles never become extinguished or burn out during the 3 days.
It's similar to the pope being instructed to consecrate Russia to the Immaculate Heart of Mary, NOT consecrating the world to her. We are to be obedient to her instructions, which have no flaws because she is a messenger from God. Unfortunately, the popes never did the former, but some say they did the latter. Either way, there was disobedience.