Cruises go every day of the year when not in drydock, many of the sailings that you mention like Bora Bora, might be a repositioning cruise, they need to get the ship somewhere else, If that is the case, they used to be a bargain.
I thought COVID would be the death of cruise ships, floating petri dishes. But no, now they are more popular than ever and charging obscene prices and they are sold out....go figure 🤷♂️