This scene is dramatic enough on its own, but recall some of the dialogue that occurs in this scene and the shots that come just before or after the brothers’ lines. Oh Dreamworks, you so symbolic and clever.
"Look, Rameses, what do you see?"
Note how he is looking down at all the slaves, and how Dreamworks makes a point of showing just how many there are. We are literally seeing it from Moses’ perspective and understanding—not Rameses’.
"A greater Egypt than that of my father."
Now we are seeing it from Rameses’ understanding and perspective. To him, the slaves are invisible, they do not exist, they are below him. Note how, unlike Moses, he looks up just as he says the line, not down. The animators also symbolically laid out the shot so that we, like Rameses, do not see the slaves at all. To him, they do not exist, and Dreamworks demonstrates this to a tee.