When we look from Earth to the Moon, we only see one of its faces, the visible face, with its basaltic seas that give it its peculiar shape, similar to that of a face. These formations only occur on one side of the moon, a fact that was discovered when the first images of the hidden face began to arrive. The question we ask ourselves is why that difference.
The answer could be in how the moon formed, something that was discovered recently. A large planetoid about the size of Mars hit against the Earth, making part of it projected into space. Some of those rocks would later become the Moon. The impact produced so much heat that part of the two stars vaporized. In that instant the Moon was much closer to the Earth that now and its gravitational orbit synchronized with that of our planet making only one of their faces look at us.
The Moon being smaller it cooled faster. But because the Earth it was still hot, the part facing our planet stayed warm for longer, which created a temperature difference between the two zones, causing its geology to develop differently. The bark of the Moon It has a high content of aluminum and calcium that vaporize slowly, to later condense in the coldest parts but not in the hot zones, which results in the hidden face of the Moon being thicker.
When the big meteorites started hitting the Moon, the crust of the thinnest visible side was easily perforated, but the thickest crust of the hidden side did not pierce so easily leaving the dark side crater free and much steeper.