I think that's the risk-reward trade-off. At the most elite levels, it'll all be about survivor bias. So even if that technique only works some of the time, those that it works on will have a better chance of becoming elite.
>BS. If that was the case, then YC would be a non-profit and they would accept everyone.
I could see the argument for the first (non-profit) but not the second (accept everyone). Filtering down to a set of folks that they think they'd be able to most effectively help would make a lot of sense regardless of reason for doing.