[xkcd-sucks]

Maybe the absence of a strong unified church which is separate(-ish) from a strong state, as the Catholic church related to European states? Like, there were religious institutions in classical Chinese civilization; the government did participate in it ("the role of the emperor is to maintain harmony between heaven and earth, he rules with the mandate of Heaven" etc); there was lots of "worshippy activities" in temple-ish buildings; the closest things to "official religion" were a bit syncretic but Christianity was also pretty syncretic in origin just presented later as something fully formed in unity; mythology overlapped with history in that mythological power structures resembled real power structures and government etc. One big difference seems to be the absence of Christian-style religious services in which a large audience listens to a preacher / regularly participates in a long shared ritual like Mass, but this is from the anecdotal perspective of comparing (very little) experience in modern Catholic churches vs received information and visiting historical sites in China