Here's why:

* Eukaryotic: Protists have a true nucleus and membrane-bound organelles, unlike bacteria which are prokaryotic.

* Unicellular: While some protists can form colonies, the vast majority are single-celled organisms.

* Diversity: The kingdom Protista is incredibly diverse, containing a wide range of organisms with different modes of nutrition, locomotion, and reproduction. This includes algae, protozoa, slime molds, and water molds.

While other kingdoms like Fungi and Plantae have some unicellular members, the majority of their members are multicellular.