As the batch size grew, it was hard for every partner to know exactly what each startup was doing. Especially since things often change fast at startups.
You could be running up against Dunbar's number (http://en.wikipedia.org/wiki/Dunbars_number) for the more social (as opposed to purely technical) aspects of what is going on at each startup. 66 startups with an average of a little more than 2 people per startup is hitting the upper limit (150) of what the human brain can handle socially. 84 startups with the same average exceeds it.
In my own experience, once a company or social grouping exceeds 50 to 150 people (the more tightly bound the social group, the lower the count), things change noticeably, so I'll be watching with interest what YC does to get around this.
That is certainly one of the hypotheses. The reason I'm skeptical is that it seems such a fashionable wall to hit that it's almost tacky. Which I admit is not a valid reason to be skeptical.
You could be running up against Dunbar's number (http://en.wikipedia.org/wiki/Dunbars_number) for the more social (as opposed to purely technical) aspects of what is going on at each startup. 66 startups with an average of a little more than 2 people per startup is hitting the upper limit (150) of what the human brain can handle socially. 84 startups with the same average exceeds it.
In my own experience, once a company or social grouping exceeds 50 to 150 people (the more tightly bound the social group, the lower the count), things change noticeably, so I'll be watching with interest what YC does to get around this.