Here's why:

* Viruses are not cells. They are much simpler structures, consisting of genetic material (DNA or RNA) encased in a protein coat (capsid) and sometimes a membrane envelope.

* Prokaryotes are single-celled organisms with a cell membrane, cytoplasm, ribosomes, and DNA. They have a much more complex structure than viruses.

* Viruses cannot reproduce independently. They rely on host cells to replicate. They inject their genetic material into a host cell, hijacking the cell's machinery to make more viruses.

In summary: Viruses are not classified as prokaryotes (or eukaryotes) because they lack the fundamental characteristics of living organisms. They are considered obligate intracellular parasites.