Also seems to fit everyone's incentives nicely. a16z & seed investors get their money back, so they at least don't have to take a loss. Ryan Hoover gets F-U money, assuming AngelList doesn't tank. Employees get enough for the down payment on a house, also assuming AngelList doesn't tank before they can liquidate. AngelList acquires a pre-made team with a proven track record for not much more equity than they would spend on the open market. Pretty typical SV acquihire.
Additionally, why would the VCs prefer cash to shares in AngelList? VCs are in the business of putting money into rising companies, I'd assume they'd much rather have shares in AL than having to return a pittance of cash to their LPs.
I'd also make a large wager that none of the founders of PH have "FU" money as a result of this deal. AL putting their scarce cash into the pockets of founders is a very very stupid way for them to invest their money. You'd much rather structure the deal to give the founders AL stock so they have an incentive to work hard for you instead of just waiting out the deal and pocketing your cash. Remember that AL has all the leverage here, they can structure the deal however they want.
I certainly can't speak for a16z in this particular case, but in other talent acquisitions the VCs usually prefer cash to shares in the acquirer. If they wanted shares in the acquirer, they would've invested directly in their funding rounds. Among other problems with taking shares, it opens them up to potential conflicts of interest (particularly relevant for a16z + AngelList), and it leads to having large positions in companies of which they don't have board seats or any significant visibility.
Ryan Hoover gets "FU" paper money in the form of AngelList shares; he has to wait for AngelList to have its own liquidity event before he gets to realize any of those gains. Still, if his own startup is foundering, that's probably a better bet than going down with the ship.
That is a fair point about conflicts, that makes sense. Still though if the cash isn't there, it isn't there. I cannot grasp a startup giving up $12M in cash in this environment unless they are absolutely rolling in dough. Doing an equity deal instead of cash is the equivalent of raising $12M at your current valuation (or whatever made up valuation you give yourself in the acquisition negotiations), which seems like a great deal.
Yes, I have no doubt in this deal the founders have "FU" paper money, but I know for a fact most shops and landlords don't accept that as payment :)