A landing puts you on shore for 60 to 90 minutes to walk a scouted, marked route past colonies, historic huts or research bases. A Zodiac cruise keeps you in the boat and takes you out among the whales, calving glaciers, rolling icebergs and penguins on floes. Most people arrive assuming they want maximum land time. A lot of them leave preferring the Zodiac.
The reason is that a landing can feel static. You walk, you look at a colony, you walk, you look at another colony, and you're mostly doing it on your own.
A Zodiac cruise is more dynamic and it reaches places that have no landing site at all, like the iceberg graveyards. You also get an hour of near one to one time with a specialist guide, and a different guide each time, so the cruises often end up being the more educational half of the day.
This matters when you're choosing a ship. If you're picking a vessel purely to maximise your minutes ashore, you're optimising the half of the day that many guests care less about.