> If they were stronger, they would have raised proper VC.

I think that is really the most important part. A lot of people sophisticated enough to have their interest peaked by the opportunity probably figure the deals being offered are (more or less) the deals already rejected by traditional and more sophisticated channels. If established but private companies (e.g. Lyft) were doing late stage rounds through this type of a marketplace I think demand would be much greater. The problem is those companies probably don't have a lot to gain by doing it that way.

Now my assumption on quality may be wrong but that sentiment seems like an important hump for these marketplaces to get over.