There are several reasons that I buy trip insurance.
I use
Travel Insurance - Compare and Buy | Squaremouth as I find their site the most user friendly and efficient.
The policies offer better coverage for less than DAN and Dive Assure.
Yes, no need to cover the cost of your flights at this time.
I do always make sure that the medical coverage is secondary. That way I'm covered for the out of pocket expenses that my primary insurer, (Blue Cross), doesn't cover.
When we fly United and purchase with my Mileage Plus card, the accompanying benefits are very good. The only reason I buy is for the medical and for emergency evacuation and repatriation of my remains. My wife wouldn't be comfortable in hauling my carcass out into the jungle.
The last time I purchased, it was under $60.00 for our trip for way, way more than enough to take care of the most catastrophic situation.
Edit to add: It's really not a big deal to read the exclusions to see if scuba is covered. Some cover to 120', some to 130'. You can also do a search to filter the results in the site I referenced