Why in 1846 would so many families from Germany uproot and come settle in Wisconsin?
I think I may have found one possible anwer to this question. On the Wisconsin webpage there is this entry about Carl Hasse and the booklet he wrote encouraging his fellow countrymen to go to Wisconsin.
A German emigrant guidebook, 1841
Schilderung des Wisconsingebietes in Nordamerika (Description of Wisconsin Territory in North America)
"Carl E. Hasse (1802-1872) came from his home near Leipzig, Germany, to visit Wisconsin in 1838. He stayed several months and wrote this 80-page pamphlet when he returned. In it he says he doesn't want to persuade anyone to emigrate to America, but only to provide accurate information based on his own experiences to people who are thinking about it. His account is among a handful of works credited with starting the large-scale immigration of Germans to Wisconsin which peaked after the country's failed 1848 revolution. Hasse immigrated to Wisconsin with his family about 1845, settling in Greenfield, outside Milwaukee. He became a community leader, serving as a justice of the peace and elected twice to the state Assembly (1852 and 1859). After the Civil War, he appears to have followed his eldest son's family to Missouri, where he died in 1872.
Hasse's pamphlet is extremely rare: only three copies exist in U.S. libraries. This one may have belonged to the author, since it was given to the Wisconsin Historical Society by his granddaughter, the influential librarian Adelaide Hasse (1868-1953). It is entirely in German and printed in the Fraktur script; no English translation is known to exist. Following the text is a large map of Wisconsin and Iowa territories, with an inset of the settled portion of southern Wisconsin, dated 1841."