Religion seems to be a kind of art-- sacred aesthetics. Comparative religion then feels like art history.
I'm reading a book by Paul Krause on Greek and Roman classics. According to him, the transition from Hesiod to Homer is marked by the transition from a worship of agon, which is a worship of passion and virility, no matter how horrible and destructive the ends, to a worship of love and piety. Piety is not even discussed in Hesiod. In Homer's Iliad, both agon and piety are explored, and piety is shown to be the superior virtue in the end, as the ravenous and powerful Achilles is won over by the love displayed by the weaker, submissive, Priam. This shift in mythology and art would reflect the shift in psychology of the Greek mind and culture.
But Paganism is unique in that it supports multiple parallel mythologies. Even after Homer, there could be those, maybe those with too much testosterone, who still prefer Hesiod, and the agonic way of life.
In Hinduism, there are many parallel mythologies. It's unclear if they were 'shifts' or just parallel aesthetic tastes. The Tripura Rahasya, for example, still reveres the Vedic Gods (Indra, Agni, Vayu), but subordinates them all to a feminine Divine Mother, reflecting a different psychology than one might see in many interpretations of the Vedas. This other psychology is: why do all these complex sacrifices to try and gain the favor of the volatile and passionate forces of nature (devas)? Surrender to God as Love, and everything will be ok. It is only your desire (kama) that subjugates you to the devas. If you do not desire, they do not have control over you.
(All this, of course, raises the question: which aesthetic is "correct"? Can I ignore ritual, trust in a loving God I cannot see, and things will work out? What does it even mean for "things to work out"?
Are the new agers right? Is it our beliefs that create our reality? Can I then choose whatever religion is my favorite, and whatever causality exists in that religious worldview will become true for me? Or is there an objective reality that each culture tries to map to symbols, and describe in their own artful ways, and some cultures are closer than others?)
Along with religion, we have mysticism. This is the path of yoga, nei gong, etc. Mysticism is much less dependent on art, myth, and culture, because it's based in universals: human anatomy, human perception, and the five elements.
The popularity of mythless mystic paths, especially yoga, is definitely in part because of our scientific materialist worldview. The belief in an objective reality, free from the bias of culture, that must be uncovered.
But I think another cause we ignore is the decline of art and aesthetic power in general. The pale Hindu priests at the Livermore temple do not inspire much reverence. Kids do not listen to the Iliad performed in dactylic hexameter. Religion declines with art.