text: The same reason nothing you ever observe is affected by the earth revolving.  It's moving at a constant velocity, meaning there is no acceleration and therefore no force (F=ma).  Force is what you feel, which is why you feel pushed toward the back seat of a car when you are accelerating (speeding up) but you don't feel it when you're moving constantly.  Like, in a vehicle, if you throw up a ball, it will come right straight down because if the car is moving at 50 mph, it, you, and the car are all moving at 50 mph.  The bird, us, the air, the tree, the worm.. everything's moving at the velocity of the earth so it is considered "at rest" because it is our frame of reference.