I saw a comment by mevaqesh:
To summarize the thesis set forth by R. Dr. Soloveitchik and in collected Essays vol. II and elaborated on in vol. III, the Ashkenazic mesorah was founded by a group of Babylonian scholars who, annoyed with the increasing liberalisation of their "mainstream" Geonic counterparts, moved to the Rhineland to start anew. Thus, in spite of a few Palestinian/ Italian influences on Ashkenzaic liturgy, their massoret in learning is a continuation of those maverick Babylonians.
I would really like to know more about this.
Could someone with access to this sefer provide a quick summary on this? What exactly happened back then, and how did it lead to the current Ashkenazi Jewry we have today?