Kuki... about 12,000,000 cruises are taken every YEAR from the US, so in a decade it is 10-times that figure.
I have done EXTENSIVE research on this topic. Most people who jump do it to commit suicide. In fact, something like 1 in 20 suicide attempts fail. However, jumping from a cruise ship is a very easy and sure way to do it and not fail. Also - vastly relevent is that the availability of a means to commit suicide makes it five times more likely for an attempt to be made (suicidal people should not keep handguns). This means that when suicidal people take a cruise the thoughts creep up and it is just too easy for them to give in.
The vast majority of "jumpers" are never recovered, because with even the slightest chop in the sea you cannot see a person in the water - they just don't stand out at all. The ones who are recovered were usually very drunk when they went over, and they say they don't remember how it happened. See, all it takes is a momentary split decision to make the irreversable act. I also believe that is why cruise ship suicides almost never leave notes - because they don't plan it out, they see the power of the sea and their thoughts get the best of them. They just do it.
Golden Gate jumpers don't leave notes either.
People who do this tend to be either elderly, depressed or young adults. The first two categories want to end their lives, (and it usually appears more planned out) but I have a gut feeling the young adults who do it act impulsively, actually thinking they will survive. They really don't understand how dangerous it is.
I think they believe the landing will be soft, and that they may see land and believe it is closer than it looks.