The craters on the Moon remain visible even though they were formed by ancient meteor collisions because the Moon lacks geological processes that could erase or significantly alter them. Unlike Earth, which has water, atmosphere, weather, and tectonic activity that cause erosion and resurfacing, the Moon is geologically inactive. It has no atmosphere to cause weathering, no water for erosion, and no plate tectonics to recycle its surface. As a result, craters formed billions of years ago stay essentially unchanged and preserved on the lunar surface.
The Moon's surface has not been modified significantly since early in its history, so all impacts since the Moon solidified have left lasting marks. Even very small impacts continue to create tiny craters since there is no atmosphere to burn up incoming particles. The relative lack of erosion and surface processes means the ancient craters remain visible as a long-term record of the Moon's history of meteor collisions.
Additionally, the distribution of craters varies on the Moon because the near side experienced volcanic activity that filled some basins with lava, covering older craters, while the far side has almost no such lava fields, preserving more craters visibly.
In summary, the visibility of ancient craters on the Moon is due to its lack of atmosphere, water, weather, and tectonics, which otherwise cause erosion and surface renewal on planets like Earth.
