Ask HN: Why is there no Web-based auction for securities offerings?

I was thinking that with sites like SharesPost creating a second market for private companies, why is there nothing like that for funding rounds? The closest thing I can think of is Kickstarter, which is limited to "pledges" rather than investments.

Arguments against would include:

- limit of 499 investors, though this is presumably easy to cap via the fact that it's an auction

- requirement of accredited investors, though SecondMarket et al. presumably contends with this already

- not knowing necessarily who the investors are; this one seems pretty tricky

- issues of disclosure, particularly if the company wants to keep its accounting statements secret; this one is especially tricky

Is there something I've missed here? Could someone more familiar with securities offerings chime in with whether this has been attempted or what the barriers would be (beyond the obvious one of getting startups and investors to actually sign-up)?

Why is there no eBay for securities offerings?