Here's why:

* Protists are a diverse group of mostly single-celled eukaryotic organisms.

* Protozoans are a specific group within Protista that are heterotrophic, meaning they obtain nutrition by consuming other organisms.

* They are not plants (Kingdom Plantae), animals (Kingdom Animalia), fungi (Kingdom Fungi), or bacteria (Domain Bacteria).

So, while protozoans have characteristics that may seem similar to other kingdoms, their unique features place them firmly in the Kingdom Protista.