Because there is no wind on the moon to blow it around.
As long as no one touches or disturbs them, footprints on the Moon will look the same, and will remain unchanged forever. On the moon, there is no wind that would cover the footprints, and there is no water or rain that would wash the footprints away.
There were recent amazing pictures released to the press of the surface of the moon which showed many of the objects left on the moon including footprints! So you know the footprints last over 40 years because it has been that long since Neil Armstrong made history with the first footprints on the moon. There is no atmosphere on the moon therefore no rain, wind or water flow so the only thing that will destroy the footprints is space debri of either man made materials or rocks such as a meteor storm. Scientist from different nationsintentionally crash objects into the moon for various studies.
There is gravity on the moon, it is just weaker than it is on Earth. There is fine sand on the moon. if you step on it, of course there would be footprints.
Ten Million Years
There is no wind, and barely any gravity so the footprints will stay on the moon for yyyyyeeeeaaaarrrrrrsssss.
The footprints on the moon left by the astronauts will still be there in a few thousand years. They will eventually be covered with new dust from micrometeorites.
The Moon has no wind, no water, and almost no moon quakes (earthquakes on the moon). There is almost nothing to cause the footprints to go away. Unless they are hit by a meteor, comet, or asteroid.
Footprints in the moons surface (so in the dust lying on the moon) will never go away because there is no wind on the moon to blow new dust over the footprints.
The lack of atmosphere means there is no wind, or rain, etc. to either erode or wash away the footprints. The only way for the footprints to be disturbed would be from an impact event, such as a meteor striking the moon's surface near the prints and disturbing the surface.
Until something disturbs it, like a future meteor impact, or a future moon landing. The footprints left by the astronauts may last millions of years.
Of course there was moon landings, there were 12 astronauts, you can see their footprints, and there are six lunar modules and flags on the moon, for doubting idiots to be convinced.
Because there's no gravity or wind.