Why have we not seen any impacts within the last 400 years of astronomy?

since the telescope was created until now, not even a flash of light was seen impacting a planet. meteors fall on earth but not a single one has been seen causing a impact crater. mars has less of a atmosphere than we do and it is far less likely a asteroid will burn in space, why hasn't a single rock noted to fall from the shy and hit the mars rover? why have since all the technology today, we have only seen one object (comet shoe-maker levy 9) impact a planet.