> edit: There's another possibility here, which is that there are two curves that may have maximized for companies around that time period. The first is the batch size, which has increased from ~10 companies to ~100 over the years. And the other curve is that companies take something like 5-10 years to mature. Maybe it's just that the companies of that vintage are just old enough to be really valuable, and that there were enough companies in the batch to push them to the top of this ranking.
I think that's basically it.
It takes a while to reach a 100M or 1B valuation, so you wouldn't expect to see many of the most recent YC companies on the list just yet. On the flip-side, YC batches were significantly smaller early on before ~2011.
Getting more popular ~2010 lures more 'big-dreamers' to flood into YC. It's the same thing as the Ivy League effect on universities where top talent chooses top universities which yield top science/business champions in a virtuous cycle. YC's actions to increase batch size, open a startup school are all going to have bigger "net" effect.
Timing-wise the web2.0 and then smartphone waves as business disruptors have their trace on the numbers as well as the prolongation of the market boom with increased venture money and the network effect of YC alumni.
Risks include a market correction, post-smartphone bets, applicants more apt to 'gaming' the YC acceptance process.
I would like more numbers on competition (other accelerators), overall startup market, and the YC batch size.
I think that's basically it.
It takes a while to reach a 100M or 1B valuation, so you wouldn't expect to see many of the most recent YC companies on the list just yet. On the flip-side, YC batches were significantly smaller early on before ~2011.
I wouldn't read too much into this distribution.