Its because okpay rules does not allow hyip investing as far as I know. So its useless to use okpay if you are planning to invest in a hyip site. I think its really going to be a good paying site if we want to make good income in here. I just don't like to see myself losing money in hyip investing using my okpay account. But I do like to use my okpay in forex trading.
I am not sure because i know of a program which scammed already,the admin has been using the payment processor before they scammed so i don't think they are not accepting hyip but just that they are not that popular as manyy investors are not using it.