Yeah, apparently Diablo was also very easy to "hack" and almost was ruined by cheating. The dev's released many patches and stuff to stop cheating, but apparently it was all in vain in the long run...
No game is 100% immune to cheating, but some are easier to cheat at than others.
Online RPG's have often run into the problem of "PK" or Player Killers. That is people who go around killing other player characters and stealing their stuff, rather than playing the game "right" and only killing AI and working to earn their gear. This is simply due to a few oversights on the part of developers (ie: they probably figured the ability to hurt other players would lend to strategy... like "oops, don't hit your buddy by mistake!").
With regard to JK/MOTS:
The single player "cheats" were programmed into the game by the dev's. Cheats such as these are great for reviewers, testers, and developers because they can allow them to test stuff and skip around the game without having to replay every single second of it.
For users who have already beaten the game or gotten bored with it, cheats are a way of screwing around and having fun or trying out whacky stunts. Oftentimes the game company will "release" these cheats to the public a short time after the games release (the logic being they don't want to do it right away so that everybody cheats and it's no challenge).
As to multiplayer cheats, these are basically mods that people have made that exploit weaknesses in the protection and peer to peer system of the games. This means they can exploit holes in the programming to allow them an unfair advantage over people who have unmodified files. Cheating of this sort is usually much tougher to do in Client/Server based online games, but it can still happen (such cheats in the Quake games like "full bright" that lets you see even in darkness and bot aiming that lets you have better aim than normal).
Contrary to what some folks believe, the single player cheats to NOT work in Multiplayer. Typing in cheat codes in multiplayer does nothing.
Yes, most MP cheats are pretty easy to do, and pretty lame. Many of the cheats have no point other than to piss people off and ruin any competition and fun in the game (such as by screwing up the level, making it so that people can't even move and lagging the game with extra 3dos).
Some cheaters seek merely to "test out" cool looking cheats, but to do so, they barge into legitimate games and ruin it for the other people there. Others seek to impress newbies that have never seen anything like this before. This explains the numerous people on the zone clamoring for people to "teach me how to hack!"
The sad fact is, that while some tried to defend the practice of "hacking" Jedi Knight by saying that it "took skill and intelligence" most of the stuff is as basic as changing one number in a notepad file and hitting "save" or whatnot. And in addition, most of the time, people just downloaded the cheater cogs off of the internet, so it took zero effort on their part to use them.
There used to be hundreds of "hax" or hacker clans (believe it or not) who featured lists of files you could download and unzip them into your Resource directory.. instant cheating!
And that is why programs like Kicker Helper were inevitable and necessary if the integrity of the game was to be preserved.
Without them, I have no doubt that far fewer people would play the games anymore, as many were fed up with the cheating and the arrogance of the cheaters.
I wouldn't call JK/MOTS cheating "hacking" although so many people have called it this over the years, the name has stuck. No reverse engineering or hex editing is done in order to cheat. No compiling, no code-breaking, etc. All that a person has to do is take any of the cog/dat files (which are in english) and modify certain values.
Most people that cheat I don't think do it "becuase they must win at all costs" or similar reasons, but rather "because they can" or they are simply bored, and with the anonymous nature of the internet, it's virtually consequence free (at worst, you'd be insulted and booted from the game).