Because we are far enough from Earth that gravity no longer affects us.
But why aren't we falling towards Earth?
Gravity is affected by the distance and mass of 2 objects. For example in outer space, the moon is pulled to the Earth because the earth is so large, but if it got too close than the gravitational pull of the Earth would pull it into us.
How does gravity work
This happens because gravity is a force. It can affect the speed momentum and movement of things under its affect