I was wondering if a possible explanation is that, due to the gravity attraction of the earth, the hot, heavy, inner part of the moon, which is richer in heavy elements, I guess, like iron is closer to the near-side surface. Since in the far-side the hot, heavy part is too far from the surface the eruption activity is small or non-existing.

Because the moon is tidally locked to the earth the pull always act in the same direction.

I was imagining the moon as a drop of liquid in the vacuum space with a denser core at the center. The heavier core would be at the center because of the moon's own gravity. In the presence of the earth's gravity the denser part of the "liquid drop" will be centered more closely to one side and so the volcanic activity would be strongly biased.