Several threads in these forums begin with some sad tale and then post after post pounds the hapless travelers for not buying trip insurance. I'll admit on our first cruise I did not buy travel insurance. As the time of our cruise drew near I began to think that it might be money well spent, so I called my TA and she told me the time was too close to the cruise and I couldn't buy insurance now - they would think I was looking or a cheap way to cancel. Whether that was correct or not is not the question.
Why don't people buy trip insurance? I'm sure there are many answers. The first thing that comes to mind is the most obvious; the money you don't spend on insurance can be spent on vacation - right? A penny saved is a penny earned.
But I expect the biggest reason is that the nature of the investment in a cruise, tour or (maybe) resort vacation differs from the typical vacation. So people just don't think that the insurance is necessary. On a typical vacation if I get ill before I go I call the airline and hotel and cancel my reservation. Even if the airfare is non-refundable it can be reused for a fee, and I may have to eat a night's lodging at the worst for canceling the hotel. And, I never spend a dime on food, entertainment, amusement park tickets, etc. If I need to cut my vacation short, the airport is still there and I can easily go home - or if my stay needs to be extended the same story applies.
Not so on a cruise. First, you have a very large sum of money wrapped in up in the cost of cruise itself. Second if you need to cut your trip short you are not anywhere near the airport where your return trip is supposed to start. And finally (but probably not last) you are probably in a foreign port and your health insurance may be of no value to you.
Just some thoughts.