I would guess most peoples concern is that you don't have a track record and are asking people to trust your programming: "Our algorithm tried hundreds of thousands of combinations of variables and combinations of filters to give the ones that give the best return." P2P-Picks is/was probably different as the author has a known background (podcast interview by Peter(LA), stats background, etc), has a commercial product, few years of performance history, and work with each drop.
I waited a several day to respond. In my order of preference.
1) FICO
2) Employment years
3) Credit Utilization
4) Months since Last Delinquencies
5) Income
6) Loan Amount
7) When originated (i.e. how long ago did the loan get originated - days since first showed up on one of the 4 drops)