I don’t think greed is the main reason, they fall for these scams mostly because of stupidity.
Greed is one thing, but if you're smart, you’d still know how to manage the risk. But plain stupidity? That leads straight to regret.
I think Crwth is right, greed is one of the main reasons people fall for ponzi schemes. As we know, ponzi comes in form of high yield investment opportunities. Because greed is some person's weakness, the allure of quick and easy money can cloud their judgement, making it difficult for them not to recognize the warning signs and stay away from such investment. They invest their hard earned money and suffer huge financial loses.