One hint about the history of Yiddish may be the Protestant Reformation in Germany. Jews were caught in the middle and persecuted by both sides, especially during the early stages when whole synagogues were surrounded and given the choice of mass conversion or mass burning. The whole Rhine Valley and border areas between Protestant and Catholic areas such as Lower Bavaria seem to have been especially turbulent.
I have ancestors named Kissinger, originally from Bad Kissingen in Bavaria, who were in Rhein Hesse in an area that went back and forth between Bavaria and other states. Consequently they also switched back and forth between Catholicism and Protestantism whenever the borders changed. My ancestor Matthias Kissinger was born a Catholic, married as a Catholic but came to
America as a Lutheran in 1737 because the local ruler had converted to Lutheranism.
As far as I can tell, all my German ancestors were refugees from war torn areas such as northern Swtizerland, Alsace, Rhein Hesse and northern Baden-Würtemberg. Most were in the area between Stuttgart and Frankfurt at the time they came to America c. 1720-1740.
I'm sure that in such a cauldron of religious hatred that persecuted Jews got out as fast as they could unless they were under the protection or sequestered by local rulers.