Because Covid.
https://www.langerresearch.com/wp-content/uploads/1216a52020StateBattlegrounds-MIWI.pdfQuote:
A surge in coronavirus cases has damaged Donald Trump's re-election campaign in Wisconsin, with growing criticism of his work on the pandemic and preference for Joe Biden to handle it. Biden holds a slighter advantage in Michigan, with sizable leads among women, moderates and independents in ABC News/Washington Post polls in both states.
Biden leads Trump by 57-40 percent among likely voters in Wisconsin, a state that's now reported to be third in the nation in per capita COVID-19 cases, with a 53 percent increase in average daily cases in the past two weeks, a record number of hospitalizations and a 112 percent jump in deaths. That compares with a closer 52-46 percent in mid-September.