As a travel agent who has been booking cruises for fifteen years I thought I could give some points

1) Most cruise lines close the sale of the specific sailing 48-72 hours ahead of time as they have to transfer the reservation information to the ship and also allow TSA/CBP time to scrub the list.
2) Vacations-to-go's site is a static booking site that does not show real time availability. They may list a cruise on their site, but it may not be still actively selling. As you can see, you can't book anything on their site as you have to call their call center to get the most up to date pricing and availability.
3) As Often1 said, large agencies due to acquire large blocks of cabins on a ship through group contracts. They do not actually buy the cabin but enter into a contract with the cruise line that will hold a specific number of cabins at a specific price. Most of these contacts are done right when the inventory is released. If the prices on the sailing goes up, we get to sell our cabins to our clients at that lower contracted price. If the pricing on the cabins goes down, we book the cabin at the public price.
- The cruise lines will recall any unsold cabins in these group between 90-120 days before sailings.

Once the cruise goes past final payment date, the cruise line is in control if the pricing goes down. Many of them have stated that they were cutting back on the fire sales as they want to promote people booking early than last minute.