Here's why:

* Bacteria are prokaryotes: This means they lack a true nucleus and other membrane-bound organelles. Their genetic material (DNA) is located in a region called the nucleoid, which is not enclosed by a membrane.

* Eukaryotes have nuclei: Eukaryotic cells, like those found in plants, animals, fungi, and protists, have a nucleus that contains their DNA.

While bacteria lack a nucleus, they still have other essential structures like ribosomes, cytoplasm, a cell membrane, and sometimes a cell wall.