Urbanization matters.
“If on politics we have a bit of a mix between decline and continuity, when it comes to the cities that made up the old political system, the ‘decline and fall’ knight strikes a clear blow: the system of social organization that characterized the ancient world practically vanished and would have to be redeveloped centuries later. The institutions that had maintained it (like the curiales) largely vanished, replaced in some cases by local ‘notables’ and in other cases by ruralization.”
https://acoup.blog/2022/01/28/collections-rome-decline-and-fall-part-ii-institutions/