There are a good number of reasons why some speculate that the moon is not a moon at all, rather a huge base for aliens.
1.Ancient people who captured history in writings and pictures left out the moon in their documentation.
2. Some say the moon did not start to illuminate until 1977.
3. The moon rang like a bell for a long period of time according to the astronauts on when they landed (if they did).
4. There are quite a few places on the moon that look suspiciously like created structures.
5. The astronauts have seen aliens on the moon and reported it to NASA.
6. The moon never moves. The dark side of the moon is never seen by us on Earth. Strangely enough the moon is not rotating or moving at all even though it should be.
7. Corey Goode (Cosmic Disclosure) claims that it is an alien space station and that he has been there before.