It has a lot to do with the patterns of the
Yankee diaspora [migrants whose first ancestors settled in New England). The Yankees were the Pub base back in the 1920’s, as it had been since the time of Lincoln. All of Michigan was in that diaspora zone:
The map appears in
this chapter. Yes, I know, we think of Germans when we think of Wisconsin, and Scandinavians, when we think of Minnesota. They came later. When I have time, I am going to listen to all the podcasts. I love this stuff.
Oh, here is a more accurate map of the reach of the Yankee diaspora, which also happens to be the zone that is littered even to this day, with small liberal arts colleges (many of which being of very high quality), almost all of which were founded by Yankees. New Englanders had the highest literacy rate on the planet back then, and valued education.