Why do animal and plant cells lack cilia flagella or other means of locomotion?

Cillia and flagella are used for motility. Most cells of animals and plants do not need to be mobile, but small uni-cellular or organisms of few cells do. But it is not true that animal cells do not have cillia and flagella. Sperm need to be motile so they have flagella. Your lungs need to clear dust and small particles from them so they have cillia.