I think we outgrew it — the need for special shares that founders could sell in the next round. Or put differently, it just became a standard part of hot Series C and Series D rounds (and some Series As and Series Bs).
Series FF was a terrific idea when unicorns were rare, and getting any liquidity at all was something rare. Until 2009–2010 or so, founders rarely got to sell shares pre-IPO. It happened, but it was rare.
Remember when The Social Network was about going for it and having Facebook be worth One Billion Dollars — not just a million? Well, yeah. But Facebook is now worth five hundred billion. 500x more.
Times changed. Unicorns number in the 200s. 200 Unicorns, and growing fast. That ain’t rare.
Decacorns are the new Unicorns. Softbank raised the largest venture fund in the history of mankind to fund startups that can be worth $100b+.
And if we are honest, almost none of us predicted the rise of the Decacorns and so many Unicorns.
And with that, secondary (i.e, to founders) liquidity became much more common. Routine in later-stage deals. Almost all of them.
The idea of Series FF became commonplace. It just wasn’t called that, or papered that way.