Here's why:

* Cell walls are rigid structures found outside the cell membrane of plant cells, fungi, bacteria, and some protists. They provide structural support, protection, and regulate the passage of substances into and out of the cell.

* Animal cells rely on their flexible cell membrane for support and protection. This membrane is composed of a phospholipid bilayer and proteins.

So, while animal cells and plant cells share many similarities, they also have key differences in their structures. The presence of a cell wall is one of those differences.