I spend four years making mods for TES: Morrowind and was impressed by the games huge possibilities, so was the community.
What is the secrect? It's simplicity.
Morrowinds Editor provied you with a quite easy and intuive handling, once you took time to lean some basic controlls.
With these controlls you could built what ever you want.
Bringing life, aka Npcs and quests to the whole thing was a little bit more complicated. You had to put your mind around the questing system. But one that happend, it was really easy, all it requirred you to do was to insert text were you wanted it to be.
Scriping, for example making a banner float in the wind, when the game generates stormy weather, took the form of a small programming language that also wasn't that hard to get hold of.
Bethesda then decided to axe the modding community by making oblivion use voiceacting, which was terrible in the original game and therefore only an bullet to the modders face. (It just breaks the immersion to have your modded in Npcs not talk or talk like teenage from Bribane). They also added the fancy cry-tech-style-huge-view-distance, wihch was awesome in the first five minutes of the game, but then again, broke modder's legs, because it was hard to change the distance-rendering of the landscape, to make it show your huge mountenside-fortress, once you got further away from it than fifty yards.
This, I believe, is the destiny of all modding in Games: Once stuff gets too complicted, you can't expect fans to just jump in and fill the pieces.
LBP, I think is a bad example. The game is supposed to be a modding-sandbox. Comparing it to modding in other games, that acually are complete games, not just toolsets, makes it like comparing a snowshovel to a spoon in a snowshoveling-contest: It can do the job, but the comparison is just unfair.