It makes sense though - more people probably stumble across HN while searching for programming answers than through hearing about Y Combinator.
Even those that realise that the top left top left 'Y' image is actually a link to ycombinator.com would be hard pressed to find a link from there to PG's essays.
> I'm actually pretty surprised that there are HN users that don't know about his essays...
Actually a long time ago, I remember reading one of PG's essays on High School and was struck by the sheer number of active comments (vibing with the thoughts) on it from kids who were in high school and most likely had no idea what HN was.
I'm actually pretty surprised that there are HN users that don't know about his essays...