Satellites in low earth orbit are not quite above all of the Earth's atmosphere, so there is some small amount of drag from the extremely thin air. That drag force is constantly taking kinetic energy away from the satellite, so its orbit is constantly getting lower.

It is different for Earth. Earth is not experiencing a continuous drag force. It does sometimes get hit by meteoroids or asteroids, but not always from the same direction, so each impact is not necessarily reducing the Earth's kinetic energy.

An orbit is not a delicate balance between gravity and centrifugal force. It is a sum total of the kinetic and potential energy of the orbiting body. Kinetic energy is energy of motion and potential energy is, in the case of an orbit, energy of height. In a perfectly circular orbit both types of energy would be constant all the time. In an elliptical orbit, the potential energy is larger, at the expense of kinetic energy, at the high point of the ellipse (aphelion for Earth) and at the low point (perihelion for Earth) the kinetic energy is larger at the expense of potential energy. So the speed of Earth in it's elliptical orbit is constantly changing, as is its distance from the Sun, but the total energy is constant. To make to Earth fall into the Sun would require removing all its kinetic and potential energy, which is just so much energy that even a large number of big asteroid impacts are trivial in comparison. And remember, some impacts might actually increase the Earth's orbital energy if they hit from the correct direction.