Here's why:

* Prokaryotes vs. Eukaryotes:

* Fundamental Structure: Prokaryotes lack a nucleus and membrane-bound organelles. Eukaryotes have a nucleus and a complex system of internal membranes. This difference is the most fundamental and leads to vastly different cellular processes and organization.

* Genetic Material: Prokaryotic DNA is circular and located in the cytoplasm. Eukaryotic DNA is linear and housed within the nucleus.

* Size: Prokaryotes are significantly smaller than eukaryotes.

* Reproduction: Prokaryotes reproduce asexually via binary fission, while eukaryotes reproduce both sexually and asexually.

* Plant vs. Animal Cells:

* Cell Wall: Plant cells have a rigid cell wall made of cellulose, while animal cells lack this structure.

* Chloroplasts: Plant cells contain chloroplasts for photosynthesis, while animal cells do not.

* Vacuoles: Plant cells have a large central vacuole for storage and support, while animal cells have smaller vacuoles.

* Other Differences: There are some differences in the structure and function of certain organelles (like lysosomes) between plant and animal cells, but these are not as fundamental as the differences between prokaryotes and eukaryotes.

In short, the division between prokaryotes and eukaryotes reflects a much deeper evolutionary split and a vastly different cellular organization than the differences between plant and animal cells, which are both eukaryotes.