The most important aspect of travel insurance is medical evacuation when overseas, or at sea. The costs could be many tens of thousands of dollars. You're on a stretcher, clinging to life by a thread, and need immediate evacuation to an appropriate medical facility. It's not a good time to be hung up on costs.

Second is medical expenses. Using your domestic health insurance in a foreign country can be challenging, expensive, and it may not actually cover some things - or anything. Medical costs are likely to be a lot less than in the US, but could still run into many thousands of dollars.

Airfares, hotels and cruises can be tens of thousands of dollars, but you can probably get some of that back, your credit card or other insurance may cover some of it. And, you can LIVE without that money. You have time to figure it out and work things out. Still, nice to have it covered.