Main reason people cheat in MMOs is simply because:

A) They are just some edgelord looking to be a showoff curbstomping everybody
B) They don't have much time for gaming
C) Because they can.
D) Rare reason probably they want to know how the game works
E) Rare reason they want to explore for unused Content (there is people like this)
F) They're some kind of farmer, and sometimes real money is involved.

Group A and F is the most likely cheaters that populate most MMOs