Your baby chicks poo so much because they have to eat a lot to grow as fast as they do!
Remember, they are going from egg-sized (2 ounces or so) to chicken-sized (8 pounds or so) in just a few months, and that takes a lot of energy and food. Imagine how much baby humans would eat if they grew into teenagers in just a few months! Since lots of eating means lots of pooing, baby chicks do poo a lot. It's important to keep their area clean so they will grow up healthy and strong.