its electorate is relatively old. door and leelanau also have high senior populations which is probably a more direct reason in why they flipped than tourism per se
Trump won seniors albeit by smaller margins. However in Door and Leelanau I believe a lot of the seniors are ones that moved from cities (mostly Chicago and Milwaukee in Door county while mostly Detroit and Chicago in Leelanau county) so brought their urban values with them. Would make sense though if Kent County had a lot of Baltimore and Washington retirees. Rural lifestyle but still close to city. In Canada where I live, Gulf Islands in BC and Simcoe County in Ontario get a lot of that as many seniors like the country lifestyle but want to be close to the city.
Also wonder if with COVID-19, that helped flip those three counties as some of those who work for companies that allow them to work remotely left the city for those counties.