It's money and laziness to make it intuitive. The last true example of a level editor for a fully realized game was forge for the halo games. You could also consider Mario Maker a level editor although it's nit attached to a game, it's more like the gaem itself revolves around the editor.

In any case i think laziness to make it intuitive is the biggest factor, companies don't want to spend a month or two to make a usable editor with an intuitive ui out of the one they use themsslevs since they can't just release the one they use since it would give away too much of their precious "power" over the game assets. So that would be time to spend on a deliberately neutered editor with a goood UI that could take a good few months out of dev time.

See the problem now right? It's nit that it isn't possible, it's just laziness and greed.