Here's why:

* Bacteria and archaea are classified as prokaryotes. These cells are simpler, lacking a nucleus and other membrane-bound organelles.

* Eukaryotes are a separate domain of life that includes animals, plants, fungi, and protists. They are characterized by having a true nucleus that contains their genetic material (DNA) and other membrane-bound organelles.

Let me know if you'd like to know more about the differences between prokaryotic and eukaryotic cells!