As we know, interplanetary space is not completely empty. This would cause a drag to Earth, spiralling it towards the sun in a long enough timescale, which appears to be what has happened for many exoplanets. Also, gravitational radiation emitted by Earth is another contribution to decaying orbit.
On the other hand, there are several mechanisms which would counteract this. Mass of the Sun is decreasing due to nuclear fusion, and the photons which hit Earth concentrate a resultant force of $10^8$ Newtons, away from the Sun.
Taking all into account, what is the rate of orbital decay of Earth? It sounds like an incredible coincidence to me, if all these effects would completely cancel each other out.