Golf carts, side-by-sides, and ATVs are the most common uninsured vehicles in Michigan, because people reasonably assume they are "part of the house."
What a homeowners policy typically says
Most policies exclude motor vehicles, then give back coverage for vehicles that are not subject to registration and are used to service the residence or to assist the handicapped, and for golf carts used for golfing on a golf course. Read that carefully: a golf cart driven from your cottage to the boat launch, or an ATV on the trail behind the house, is outside the give-back. If it hits a child, there is no liability coverage. If it is stolen from the trailer, there is no property coverage.
Michigan's ORV rules make it worse
Michigan allows off-road vehicles on the shoulders of many county roads, and many Northern Michigan townships have passed ordinances permitting golf carts on local streets. Legal to drive does not mean insured to drive. Once the vehicle is on a public road it is a motor vehicle in every sense the policy cares about.
The fix
A recreational vehicle policy covers liability, physical damage, and often the trailer for a small annual premium. It also lets your umbrella policy sit on top of it, which it cannot do for a vehicle with no underlying policy. If you have an umbrella, an uninsured golf cart is a hole in it.