Below are few reasons , I think that contributes to , the cause of HYIP sites not being legit .
1. When there is more withdrawal request than deposit .
Hyip sites pays users a certain percentage of the deposited amount . At first , they may start , paying investors with their own money , in order to get audience . when more people start joining the site , they will then , start paying with what people deposited . thus when there is more withdrawal request than , deposit request , they will seize paying , because they also want to make their own profit .
2. There are some of them , that starts with the intention of scamming people . once they made enough gain from peoples deposit , they will close the site .
What are your own opinion on this issue ?