I have long "self-insured," meaning I took that risk that if I couldn't proceed with a trip or had to cut a trip short I would expect no refunds and pay my full expenses out of pocket. More recently, I found one reason to buy travel insurance: Trip Interruption coverage in case I had to quarantine in an expensive hotel for five days. Now that fewer countries are requiring Covid testing, this seems less important to me. Even then, there is a cap on reimbursement, so is it really worth it? Trip Cancellation coverage typically has many restrictions/limitations, and you may be reimbursed less than 100% for cancellation. I recall reading of liveaboards canceling for reasons that didn't fall within any of the reasons listed on the policy, so insurance wouldn't cover it. The divers had to deal with whatever compensation the liveaboard offered.
I wish travel insurance were available a la carte, so you could buy ONLY Trip Cancellation/Interruption coverage, for example. (I DO buy medical-only insurance because my US policy doesn't cover many things out-of-country.) They way "travel insurance" bundles coverage seems to me to obscure the cost of the coverage that is important to me with coverage for events that I would gladly self-insure against. There are ways to get at least partial compensation other than through insurance. You can typically cancel an airline ticket and rebook it within a year. Airlines offer compensation for lost baggage and severely delayed flights. Homeowners insurance will often cover lost or stolen dive gear. Liveaboards will usually at least give a voucher for future trips. Dive resorts may do the same or similar. Hotels have cancellation policies. But there are scenarios that fall through the cracks. We have all read accounts on SB of someone having really bad luck, like the lady whose liveaboard canceled on her while she was already on her international flight there and offered some kind of lame compensation like a land-based week.
I have insured a few big trips, where I paid in advance for a package of some kind, such as a dive resort or liveaboard. More often, I put trips together myself and self-insure the pieces. I always buy my airline ticket myself, sometimes using points. As I see it, losing money on travel is a risk we take in this hobby. In my mind, I consider such expenses as built into the cost of the hobby, just as I do with having gear serviced/replaced. The best advice--which I don't always heed myself--is to insure against things that would cause you real financial hardship if you didn't receive compensation, and just suck up the rest as the cost of doing business (or hobby in this case).