Why don't the P2P companies raise seed funding from venture capital or angel investors to put into the P2P loans?

I think that some see themselves as platform operators first and foremost, but I agree that the margin would appear sufficiently attractive to employ some ‘proprietary’ funds (there would also be potential informational advantages). This is probably an evolution waiting to happen with the advent of virtual banks and digital banks...

Regarding the questions on why they don't raise money from VC/Angels, one of the reasons is that VC themselves have their own investors to account to and are looking for businesses with 3-5x ROI (or even way more). Unless a company has a potential to deliver that ROI, it is highly unlikely that VCs will provide funding to them.