Boat US Insurance used to report their claims and payout amounts every year. By far, the majority of claims and the majority of payouts were "water encroachment" - i.e. sinking or swamped boats. (if I recall, the 2nd most claims were fire caused by 12v electrical shorts, but I could be wrong) I know for a fact that 4 boats (and I'm sure many more I'm not personally aware of) that had been taking on water in their slips at APM over the last few years were saved when someone saw and reported the problem and the boats were able to be floated before entirely sinking. I'm guessing this happens more than we all know at the marinas.
APM has security personnel who walk the docks daily looking for such problems. Boats on a buoy, unfortunately, don't have that kind of visual traffic. Further, even a relatively small water leak on a buoy moored boat can turn catastrophic if the batteries go dead and the bilge pumps stop doing their job. Just going back to business basics, you know the insurance companies would not be turning away the business if they were making money on this market segment. I'm sure if we could see the numbers behind their decision to move from this market segment, it would make sense, at least financially.
As the owner of a 40-year-old boat, as I've previously written, technically I have insurance, but practically, anything on my boat older than 15 years is specifically "not" covered - except in a total loss claim. I know, makes no sense. It sounds like I'm one step away from where many of you find yourself today with no access to any insurance, not even the NPS required liability coverage.