Read your last sentence. Then re read your question. Then really think about that you are a WARLOCK farming helium on the moon. Then let it sit in you are asking about the fact the the moon surface isn't realistic regarding gravity.

Perhaps the Traveler put a super dense material at the core as part of the terraforming process? Here is something to wake the Hive, on the subject of the Moon. Have also seen the argument about the Moon not having an atmosphere. Look towards the horizons, next time you are there. There is definitely some sort of atmosphere, there. It is thin, but you can definitely see the bluish coloration. Don't care if it is all based on real science or not. Games are not exactly known for scientific accuracy.

It would be annoying to have to get use to a different hight of jumping for every planet you visit, so it is just easier to make them all the same, then you dont add another heading for no reason. Here is a potential explanation, since it is the future you are able to generate a kind if gravity field, that can be made higher or lower depending on the situation, it automatically does this, and is meant to always make if feel as though you are on earth, so then while in the middle of combat you dont have to worry about jumping and floating away. I put this as a reply, then realized it would be better to put it in my actual post

Reasoning is probably buried in the Grimoire somewhere. Stupid Bungie trying to make us read and such.

It's a game......