[hgoel]

The unevenness of the gravitational field on Earth is for the most part ignorable. It isn't like maneuvers are precise enough that one could account for it in the calculations anyway.

Space is empty enough and engines imprecise enough that for orbital stuff you have enough margins to correctly predict and plan a trajectory ahead of time, and just do correction burns later if necessary.

On the Moon the gravitational field is indeed uneven enough to matter, but exactly one orbiter really cares about it (LRO iirc has a specific orbit where the unevenness mostly cancels out), most simply rely on occasional station keeping burns.