Here's why:

* Tidal Locking: The Moon is tidally locked to Earth. This means that the same side of the Moon always faces us.

* Rotation and Orbit: The Moon rotates on its axis at the same rate it orbits Earth. This synchronization causes the same side to be perpetually pointed towards us.

Therefore, what we call the "dark side" of the Moon is actually just the far side, which is never visible from Earth. We've only been able to see the far side thanks to spacecraft that have flown around the Moon.