Here's why:

* Prokaryotes are simple cells: They lack the complex internal organization found in eukaryotic cells.

* DNA is free-floating: Their genetic material (DNA) is located in a region called the nucleoid, which is not enclosed by a membrane. This means it's not separated from the rest of the cell by a distinct nuclear envelope.

* No membrane-bound organelles: Prokaryotes also lack other membrane-bound organelles that eukaryotic cells have, such as mitochondria, endoplasmic reticulum, and Golgi apparatus.

In contrast, eukaryotic cells do have a true nucleus where their DNA is contained and separated from the cytoplasm by a nuclear membrane.