David, many people buy insurance and lie hoping they do not feel ill. On the long 35 day cruises, at least 15 to 20 people are taken off and left in a port to get home alone. If you have not covered for pre existing conditions, this is going to be expensive when the hospital bill is added to flights etc. I use Staysure and tell them about all the symptoms i have.
It is fairly obvious some passengers take a chance when you see they are very ill and with cancers etc. No one would insure me when they were investigating bowel cancer and Parkinsons disease but i have been found to have neither but that took 3 years investigation. I could find obscure insurers but they wanted many 1000s of pounds to cover.
At the embarkation, they ask for you insurance contract but you also have to show it when booking.
Some of the evacuations from ships involve very large helicopters when 100 mile offshore and the patient has to pay