If the moon split off from the earth way back when:
The near side was once part of the inside of earth, thus the vulcanism.
The far side the outside of the earth, but without the benefit of weathering to hide the meteoric scarring or plate tectonics to create mountains, etc.
Just expounding on a theory.
The current theory is that the primordial Earth was struck by a Mars-sized planet, creating a debris field that became the Moon. Pretty much all of the materials would have been liquified, and even solid debris would have been absorbed by the coalescing bodies.
The Moon is far enough away that it does not receive much in the way of shielding from Earth. Even if you assume that the majority of objects that strike either are in the ecliptic, that’s still only about 2 degrees of coverage out of 360 - less than 1%.
However, when the Moon was formed it was much, much closer. Close enough for any number of effects, including the shielding that doesn’t happen now, as well as tidal stresses, mass transfers, etc. So the Earth could easily have been siphoning out the guts of the Moon at that time, resulting in the lava plains being created and sustained over the first couple of billions of years, and erasing the meteor craters that might have been created during that time. Over time the Moon has receded from the Earth and all of the effects I listed have moderated.