A ferry is dense. It packs a lot of people into a small space on boats that were made to effectively haul people between two docks at a relatively short distance.

A cruise ship is huge, and given the amount of amenities they host, the density of PASSENGERS on board is vastly lower, yet has a lot of added weight from service crew, pools, dining halls, water slides, slot machines and what not.

Ferries can be electric too. Never heard of an electric cruise ship before.