Some users cheat for many different reasons, some like to cheat to ensure they are playing at the highest level with limited game time, this is for those who are unable to play the game 12+ hours a day to become naturally good at the game, so they cheat instead.
Many others, especially in games like CS:GO just like to cheat to be "cool" or show off in front of there friends, this all comes down to whatever type of "cheater" you are.
Cheating has been around forever and will always be around.