Sorry, my first thought was that it requires more delta-v to enter a lunar capture orbit since the gravity is weak, but I just double checked the delta-v roadmap and it's actually not that high.

However, it is a bit problematic that landing a rocket on the lunar surface can kick rocks around the planet (thanks to the low gravity), possibly into orbit or beyond (which could pelt other equipment). So you need to switch to an entirely different propulsion system for descent, which carries a payload penalty.

https://upload.wikimedia.org/wikipedia/commons/9/93/Solar_sy...