Here's why:

* Prokaryotic vs. Eukaryotic: Bacteria are classified as prokaryotes, which means they lack a membrane-bound nucleus. Eukaryotic cells, like those found in plants, animals, and fungi, do have a nucleus where their DNA is housed.

* DNA Location: In bacteria, the DNA is located in a region called the nucleoid. The nucleoid is not enclosed by a membrane, so it's not considered a true nucleus.

* Other Differences: Besides the lack of a nucleus, prokaryotic cells also lack other membrane-bound organelles found in eukaryotes, such as mitochondria, Golgi apparatus, and endoplasmic reticulum.