Cruises have two major benefits (for the owner) over resorts:

1. Their workers are half a step up from indentured servants.
2. Land is expensive.

There are cleaner fuels available, but they cost more, so it’s only used when not in international waters as mandated by the government of wherever they’re going. Until we, as a worldwide collective, agree to stop selling and using bunker fuel, there’s not a lot that can be done, because cruise ships are basically free money for their owners.