Our previous moral system featured trust, loyalty, reputation, responsibility, belief, fairness, etc. While these features were sometimes in short supply, on the whole it provided us with an underlying and nearly costless structure to our social and economic interactions. Our new moral system is that of the dominant global marketplace. This new system emphasizes transactional, short-term interactions rather than long-term relationships. All interactions are intensely legalistic, as in: nothing is assumed except what is spelled out in the contract. Goodness is solely based on transactional success and therefore anything goes, as long as you don’t get punished for it.
In this moral system, every social and economic interaction becomes increasingly costly due to a need to contractually defend yourself against cheating, fraud, and theft. Worse, when legalistic punishment is absent/lax, rampant looting and fraud occurs.
Given the costs and dangers of moral decay, it’s not hard to see why it can cause a complex empire/civilization to collapse.