Once final payments are made for a given sailing, usually 75-90 days before, people who were going to cancel already have. So, the cruise line looks at how many cabins are still unbooked. Then, they adjust prices accordingly. But, that is only if they are underbooked and they go back up fast. If you find what you want at a price you like, book it. Waiting for deals is a form of pre-cruise gambling!
Marty