I think the biggest reason was the fall of the imperial.
Outside what is now known Italy, many Roman outposts only had a glimpse of Roman technology and as they got conquered by their enemies, everything got destroyed and the knowledge was lost in that part of Europe.
It is impressive to read books like Herodotus and realizing Greek students that could afford it where doing "internships" in Egypt, where the idea of specialized doctors was already a thing.
Outside what is now known Italy, many Roman outposts only had a glimpse of Roman technology and as they got conquered by their enemies, everything got destroyed and the knowledge was lost in that part of Europe.
It is impressive to read books like Herodotus and realizing Greek students that could afford it where doing "internships" in Egypt, where the idea of specialized doctors was already a thing.