It is hard to see any rhyme or reason in it, at least so far. The high and fast increases are mostly in rural parts of the state, but it is too early in the year to blame tourist season for speeding the spread. It is happening mainly in areas that are likely to have high vaccine hesitancy, but that's probably not a big factor yet because all supply is getting used. Restaurants opened six weeks ago, so that may be a factor that is worse in places with more skeptical attitudes about mitigation efforts. But it can be hard to draw any conclusions from some of these areas because of the small populations. My county is the most populous of the ones that are really struggling right now, with 160K residents, but some of the northern counties only have 20 or 30K people in total so a relatively small cluster can make for a very large cases per 100K rate. A few are so small that you basically just have to discard the data entirely; right now, there's a county that has had 3 cases this week, which translates into a rate of 47 cases per 100K. Last week their rate was 0, and it probably will be again next week if history is any guide.
Some of the more urban/suburban counties are seeing increases as well, but slower and more gradual. We're still not doing much genetic sequencing, so it is hard to know if a particular variant plays any role. Four cases of the UK variant have been identified in my county, none of them apparently connected to one another, so we know it is out there but no clue on overall prevalence.
A recent article in the Detroit paper blames school sports, specifically basketball, for many outbreaks, which is consistent with what we've seen in our local schools. It is basically a contact sport, has to be played indoors, players don't keep their masks on properly because they tend to slide down or get dislodged during play, and we have a lot of kids who play (for example, the local high school has boys' freshman and both boys' and girls' JV and varsity teams, so 5 teams total, each with different schedules that bring them into contact with students from different schools two or three times a week). Classroom spread still doesn't appear to be a factor. The problem appears to be all the school-adjacent things where mask enforcement is lax or non-existent, like sports and buses and carpooling and going out for pizza after class.