Because the luminosity of your laser beam is far too low to allow enough photons to make the trip, and then get reflected from a kilometer-sized spot from a low reflectivity surface, and then return through our atmosphere to your eye. This can be done, and is routinely done, using a powerful 100+watt laser beam coupled to a large research-grade telescope using the Apollo laser retro-reflectors that were left on the surface in the early 1970's.