Michelle, cruise lines have changed the way they do business and now generally offer the best prices the further out you book. They used to find that dropping their prices close to sailing time made everyone book their cruise at the last minute, thereby throwing their yield management folks into a tizzy. Now, cruise lines with empty cabins will often offer upgrades to those already booked so that the rooms that are empty, and easiest to sell, are the least expensive no-window rooms in the least desirable places on the ship.
For those who book early, if the cruise line does have to drop the price of their category of room, they are usually either upgraded or offered a refund of the difference in price. Plus, booking early gives you the advantage of choosing the cabin category and location that you like, before the good cabins get sold out.