It's an aspect of Winter, not of the moon. The moment the Ice Ladies started really talking in ways that referenced their culture, the Moon has never taken a place of importance, only winter and ice, which suggests that the basic duality of the culture isn't Sun and Moon but rather life and death. Further since this culture seems to revere spirits of cold and ice that feed by stealing warmth from people, the veneration of the Sun might have more to do with the heat it gives off than the light, as that heat would essentially compare to one's own body heat (and thus lifeforce).[T]his is speculation, but my guess is this aspect of the moon[...]
Which means glass might be super valuable to them, since well made glass for (modern) homes is designed to trap infrared light within the structure, allowing the energy of sunlight to stay and warm the building rather than leaking out the way it came in.