Why do video game manufactures make cheats

Cheat codes are actually exploits included for a reason. What for? The game developers need a way of testing their product, so they include these little 'backdoor' codes to be able to jump around or quickly set the game to a certain state and test a level or area.

Just FYI, you can RUIN (i.e. corrupt) a savegame if you have a cheat code entered, as this voids the correct settings that are supposed to be recorded by a game proving you have accomplished certain tasks. Use as your own risk.