Buyers are generally hesitant because they want to get financial info and other private data to make an analytic investment decision. Given that VC-style investment are more normalized now and they aren't as based on fundamentals, investors are definitely more willing to invest without private financials BUT really large asset managers (who spend 99% of their funds on public stocks with their expansive disclosures) will not tolerate this, limiting the market. Besides, they are getting common stock, which sucks compared to the other investors who get preferred stock.

Companies don't usually want this to happen because they don't want a shareholder (who has voting and other legal rights) that they don't know or trust, and who is not aligned with them in the way that employees and VC are (supposed to be..ha).

The solution growing in popularity tries to deal with all of these by having a company organize a secondary offering, like what pinterest does (palantir does it too, twilio recently did, so do a bunch of companies). Usually this means the company knows the buyer (sometimes an existing investor) and basically gives them the info they would give a VC, except the investors buys employee shares rather than new stock - sometimes this will be asked for an investor when they are doing a preferred stock deal, and the investor will agree as an additional "company favorable" term. Important to note here too, that USUALLY the biggest sellers in these deals are the founders, so while it's a very nice thing for them to do for their employees, there's some healthy self-interest there as well =)

If they are RSU's , I am assuming they can't be sold at all in the private markets ?

Can anyone with prior experience elablorate on these ?