I don't know why people violate the rules of the contest just to win some prize as they will be caught with this stolen or copied artwork and will not be able to participate next time.You just need to play fair and maintain the art spirit of learning and trying your best but still many are derived by greed and do all these things.
When you can earn money, there will always be people that try to cheat or trick the system. It is sad that people are also cheating in art contests but eventually they always get caught; it is in both artcontests (for Duelbits and Roobet) that people got caught by cheating or enrolling alt accounts.
This is greed and they take other people's art and then only slightly edit it so I think about this will definitely be found out too if the results are not the owner's own, whatever the art contest it must be made by hand because this is a work of dedication for Duelbits who held the event but now Duelbits has changed the winner.