People scam because they are desperate on money, usually they are that situation. But of course not all people are desperate on money scamming, but if they got chances to do it, most of them will.
Exactly their greed compel them to scam. They scam because they want to get money from all sides in any form. They mold the realities, tell lies, deceive people and earn money. They want money and for that they can go for anything bad or good, that doesnt matter to them. Better for them is to get awake from their dreams of becoming rich just by scamming, they will be caught once.