I have no inside information on this but I think it may have had more to do with concerns about whether they wanted to be encouraging every YC company to take Y

I have no inside information on this but I think it may have had more to do with concerns about whether they wanted to be encouraging every YC company to take Yuri Milner's money. See e.g.: https://www.nytimes.com/2017/11/05/world/yuri-milner-facebook-twitter-russia.html https://www.nytimes.com/2017/11/05/world/yuri-milner-faceboo... Also the total funds at the time was ~$150K, aka roughly what YC was doing before this announcement: https://techcrunch.com/2011/01/28/yuri-milner-sv-angel-offer-every-new-y-combinator-startup-150k/ https://techcrunch.com/2011/01/28/yuri-milner-sv-angel-offer... (I believe the history is that at the time, YC didn't have the free cash flow themselves to invest in every YC startup).