Good-Person
Captain Junkie
When you invest and the site would not pay then you can file a dispute with Paypal for the scammer to give you back the money. The Paypal account is connected to the credit card so the scammer is also at risk (in returning the invested money). That may be the reason why HYIP are out of Paypal.
Indeed, there are many HYIP sites who do use paypal and all of those HYIP sites became scams. However, the number of HYIP sites that use PayPal are TOO SMALL and the reasons are quite obvious. Paypal does not conduct business with HYIPs and paid to click sites because they have a really bad reputation of becoming scams.