What is the reason behind the Mishnah, talmud not written until about 8-10th century AD? This delay in the writing leads to ambiguity and speculations about the actual origin of the interpretations. Is there a specific reason given by someone, or it's just because these commentary-traditions were never supposed to be written?
For example about Pirkei Eliezer:
Isaak Jost first noticed the inclusion of 8th century interpolations. According to Jewish Encyclopedia it was composed in Italy shortly after 830.[6] Scholars unanimously agree that Pirke de-Rabbi Eliezer is a work of the 8th or 9th century.[7][8][9]