NeonRacer file

"IAmTheWalrus!" I don't know how old you are but in the days of Quake 1/2/3 and the first Unreal game, most mods add nothing to do with the original game, even if the gameplay was the same, a shooter. That was the time where a professional game engine, was very very expensive, above a million dollars, so most gamers wanting to become game developers add no choice but mod existing games, so to help, some professional developers released their tools, in something called a SDK (Source Development Kit), nothing to do with the Valve engine of the same name.
This fans would use those tools, to create games based on things they liked, football games, car games, games based on movies and books they liked, etc, some modern games are old TC (total conversion) mods transformed into full professional games, Counter Strike, Insurgency, DOTA 2, Killing Floor, etc, etc.

Nowadays because DLC's have teached new players that map packs and mission packs are the "good stuff", modern gamers don't even know that mods have more potential than that. And because professional game engines are now essentially free, people that in the old days would make a TC for a existing game, is now making a commercial or free game on those engines. So the old TC mods are a dying breed, replaced with mods that are nothing but extensions of the existing games, for example in Amnesia/Soma, mods that are nothing but map packs and mission packs, in other words...free DLC's.