Considering that there's a lot of debris in space and that impacts fling out rocks into space all the time, why do we only have one large natural satellite - the Moon? Shouldn't there be all kinds of rocks in all shapes and sizes orbiting the Earth?
Earth has few and relatively tiny sattellites other than the moon specifically because of this large moon. Note the mass ratio of our moon to our planet. It is the highest in the solar system by a large amount. This one large sattellite will over time sweep up and aggregate other smaller sattellites.
Put another way, we probably did have other smaller satellites, but they've all crashed into the moon by now, or the moon messed up their orbits to the point where they crashed into earth.
The moon is by far the largest of earths natural satellites, but is by no means the only one. There are many much smaller bodies which either orbit earth or have an orbit around the sun which is extremely similar to that of earth. The moon is the most significant and largest as it is the result of large amounts of matter clumped together that was thrown off earth in a planetary collision.