Wow, Horizon Charters did not offer to defer your trip for another time? That is not nice of them.
Ultimately, it would be the boat owner who would lose money as a charter could not be rebooked. Why should Horizon or boat owner be responsible when they encouraged you to purchase trip insurance? People don't like purchasing insurance until they need it. I see it happening with patients every day, when they need emergency surgery . "I don't have insurance because it is so expensive(meanwhile designer clothes, bling and BMWs)" .... If you think insurance is expensive, see how expensive not having (health) insurance is.