Moon regolith is pretty nasty stuff. It's chemically reduced due to the lack of O2 to react with, and becomes corrosive when exposed to moisture. The absence of atmosphere, means that sharp edges of the dust particles aren't rounded off by erosion, making the dust/soil particularly abrasive. It's also positively charged, so sticks to everything.

None of that is insurmountable, but it does stack up mitigation costs.