With around 300 cruise ships, heading off on 10,000 cruises each year, there is a lot to pick from.
If you search with less specific criteria you will have a better chance of finding someone with similar requirements.
For example, you might prefer to cruise in March but February or April would be fine for you too. If you only put March in your profile and search, you could miss out on somebody that has put April, and vice versa.
The same theory applies to most criteria. You might select 'inside twin share' but a person with everything else the same as you may have selected 'outside twin share'.
Use as wide a search as possible, and then narrow it down from there.