... You know that in the real person you don't magically become stronger just from killing people, right? I mean, I just don't see the problem here: you have the option to roleplay a complete psycho who kills everyone they can (and in fact I still think you're incentivized to do that), but the game doesn't prod you onto that path. How could the lack of kill XP possibly be a roleplaying issue where in the real world every sensible adventurer would want to expose themselves to as little combat as they could while still achieving their goals?
... You know that in the real [world] you don't magically do anything, have wizards, ciphers, rogues, or any aspects of a fantasy game right? So why are you trying to bring the real [world] into the discussion?
I think Lephys got my point. Engaging in combat should reward you with improved combat abilities. I'm not someone who wants to kill every last thing in an RPG. In fact, I play RPG's for story, not fighting. But if I'm in a situation where I want to fight certain enemies, I ought to be rewarded for that tedium by improved combat abilities which will make future fights more interesting and less tedious. Since I get NOTHING from fighting in this game, I'm disincentivized to deal with it. Hence, the cheats. If they gave XP, combat abilities, some kind of advancement or whatever, it would be worth it, but as it is now, it's not.