Timing and sample size honestly seem like great explanations to me! YC probably would've funded a bunch of current big tech cos if it was founded earlier / had the reputation it does now in like 1995 or something.

I'd like to think (not because of any evidence but just because it's more optimistic) that YC does fund big ideas, there just haven't been many foundational ones since its inception due to a lack of generational / foundational tech breakthroughs or platform shifts. Maybe AI agents will change this?