Here's why:

* Bacteria belong to the Domain Bacteria (formerly Kingdom Monera). Protista is a kingdom within the Domain Eukarya.

* Protists are eukaryotic organisms. This means they have a nucleus and other membrane-bound organelles within their cells.

* Bacteria are prokaryotic organisms. They lack a nucleus and other membrane-bound organelles.

So, while both bacteria and protists are microscopic organisms, they are fundamentally different in their cellular structure and evolutionary history.