Why is cell wall not present in animals?
Animal cells do not have cell walls, because cell walls make cells rigid, reduce the flexibility of cells, and that would affect animals from moving. Cell walls reduce the locomotive ability of organisms.
Cell walls, which are found in plant cells, maintain cell shape, almost as if each cell has its own exoskeleton(a skeleton for each cell) . This rigidity allows plants to stand upright without the need for bones.
It is generally an advantage for plants to stand upright and grow as tall as possible. Plants need sunlight, so growing taller than neighboring plants make it more likely that the plant will survive and successfully reproduce.
For animals, height is not that important, but the movement is. Having a cell wall around each cell means bad movement, or impossible to move at all. So, this means, with a cell wall, animals might not be able to move at all.
So, plants have cell walls as they don't move. But animals cannot have walls at all, because, that would prevent them from moving freely.