When it comes to cheaters (remember cheater is someone who is using additional software to gain an advantage over other players, hacker... just look at anonymous )
They do it for a few reasons - they are bad in the game and they want to play better without spending the time to get a true skill. Even few cheating software are using this as their slogan (why waste time on training if you can be better than pros with our cheat). - trolls, they just want to make you mad, it gives them that feeling that they achieved something by ruining your game - emotional issues - they are just kids and they want to be "cool"