I have flown over Lake Michigan many times, at night, in IMC, and while picking up ice. All of this was in a well equipped twin. First, there are actually very few boats or ships on the lake. Most crossings I have never seen one, so the hope of ditching near one and being picked up quickly are poor.
If you survive the ditching and can get out of the plane, don and activate your life vest, find your plb, you will be lucky. Lake Michigan can have swells of 20 feet, and seem like the middle of the ocean. You and your pax will separate and drift apart quickly. Do they each have a plb?
In 70 degree water, what is the mean time of consciousness and what is the mean survival time. How long will it take to activate the SAR assets from Michigan and get them to the area of your last known position? How far will you have drifted apart during that time? Are you carrying smoke, signal mirrors, flares, or even a whistle or light on your vest?
Two years ago while crossing east to west (never below 9000 even in a twin for me), it was intermittent IMC, and we heard a guy in a Cessna crossing at 1800, scud running at around 1000agl across the entire lake. Didn't Kimberly cross the lake with someone she had never flown with before in a rental plane she had never flown in previously? And returned Vfr at night?
My guess is that most of the pilots who cross the lake in a single (let alone at night or low altitude) have not been flying long enough to have had a mechanical failure in flight. However, if you fly enough years or hours, even a well maintained plane will have something go bad inflight at some time, and over the lake, especially at night or at low altitude is a situation where even a minor failure can start a cascade of worsening events.