I think that with teh mechanism that these sites operate on, and taking money from one person in order to give to another person, that in itself is a scam by definition and as a result i think that these websites, in my opinion, actually start off by wanting to scam people.I have read many negative reviews about HYIP sites , and I can say that it is attributed to the fact that they operate through ponzi scheme.
That is , they collect from Peter to pay Paul , and once there is no Peter depositing , Paul can't be paid.
Few HYIP sites that closes is never becomes they want to scam people , some are as a result of Withdrawal request greater than deposit.
Thus , hyip sites can be long lasting if they can invest in a business that will be yielding money. For example , a hyip that will pay in a week intervals can put the money into business that Involves daily sales . At the end of the week ,they collect their own profit and pay back the users share . With this , hyip sites can be sustained.