>>63950625
Another way to look at it is that the Roman Empire, for how impressive it was, was mostly impressive because it was coalescing the wealth of the entire Mediterranean into a single country which allowed it to not only push tech but also infrastructure to a wide degree.
After the fact, nations were too small and fragmented to do the same without either improving tech or going empire later on. The ball took a lot of time to get rolling but the results, particularly in things like armor, weapons and defense infrastructure are obvious.