It must be a tradition, or an old charter or something.
If the aliens have not crossed the dark lightyears to visit us in this reality, it is because our central buildings of government are all too large. We need to replace them with something scaled down, preferably constructed from wattle and daub so the visitors can feel superior about their own advanced technology. They have self-esteem issues and may be suffering from an edifice complex.
Right: No tiny buildings underneath
so possibly not an alien spaceship