Although it's still a point worth making that those technologies were adopted, they were not innovations--they were eastern inventions from antiquity that were adopted.

Stirrups in particular are a fascinating tale of progress not being a sure thing. The stirrup predates not only the fall of Rome, but the founding of Rome. Despite constant trade with the Parthians/Sassanids as well as constantly getting killed by their cavalry, the Romans never saw fit to adopt such a useful technology. Like the steam engine, we see that technological adoption isn't so inevitable.