The real reason: It's old.
The main reason why you get banned for unlimited credits, money etc is because when you don't buy it the legit way you make a request to a server and it gives you, but the actual legit way the website request the server to give it to you. Now when you request the server the server gets confused and gives it to you but it will make error report and when the person who manages the server he see this you are banned.
The real reason: It's old.
We must fight Dark Magic with Light Magic!