why do people hack?

Because people are bad, because they wanna troll or because do not wanna grind/waste IRL money...
Cheating can be in singleplayer/multiplayer games... just in singleplayer games nobody cares...
For me playing casual game or game with friends have no point in cheating because kills the fun playing with your mates and testing your real skills...
Hate to play PVP games with speedhacks/aimbots/etc...
For example used to cheat in Five M, roleplaying game where there's nothing competitive or needed to be cheated but trolling other players/servers or giving money etc is cool. So yeah, trolling others is fun...
Most of the times try to cheat F2P games only in-app purchases if possible for the said game because cant afford to pay money for this sh*t. In-App purchases are supporting developer right? If developer wanna be supported will make game paid and will pay for example 50$ for the said game. if its Free 2 play then adding grind/limitations/2nd currency and cool stuff that you can endlessly purchase and spending real money is not ok.