Why is it so hard to go back to the moon?

They make it hard! There's a lack of understanding of the motions of the Earth and Moon. It's thought that the Moon orbits the Earth; but in fact the Moon is stationary - only the Earth moves. Yes, I'll be mocked for that statement - just as Copernicus was ridiculed by the Church. A stationary moon means that we can travel directly to it - in a very short space of time.