There were also immaterial bases for it. Roman ideology had no explanation for life in the empire in general, not just its negative/cataclysmic turns. Republican Rome was martial, democratic, austere, industrious, superstitious, blindly traditional, blindly patriotic - the Mos Maiorum. Imperial Rome's elites were bathed in luxuries without needing to work for them - they had no use for war (even conquest only upset stability and the military was guarding borders, far away), no use for hard work, no use for democracy, no use for civic duty. Roman traditional polytheism lost all authority. Roman philosophical traditions - stoicism and epicurianism - had no appeal to the non-elites, because even though they rejected useless luxury and unjust inequality - they dictated acquiescence to the status quo. Christianity and other Eastern mystery cults promised explanation, change, active rebellion against existing life under the empire. Once the Empire began to collapse under waves of crises - conversion to Christianity skyrocketed, and the elites had to co-opt it to stay in power.

...But the reasons behind the immaterial worldviews shifting were the material changes from tiny soldier-farmer republic to massive slave-plantation/mercenary army empire.