Michigan isn't the only state with a significant Muslim population. How many can Muslim and leftist votes can Biden afford to lose on a national level? To your other point, Biden is running to the right of Trump on immigration in a desperate attempt to court those voters. It hasn't gone over well.

NH, OH, FL, MN, NJ, CA, IL & TX all have significant Arab and or Muslim American voters, many are traditionally Republican btw. Muslim Americans when not concerned about Gaza or Muslim Ban tend to be social conservatives.