I disagree with Melbtone - not all ......solos spend less (in total) than couples. I have sailed alone and spent/booked excursion for safety reason, booked specialty restaurants I wanted to try out because when I travel with companiions, some members of the party was not interested in specialty dining because of cost or various other reason etc, so this is my chance to do what I want to do.
You think you would want more people crusing? You make a profit in what you sell!!!