Yeah it's a good question to ask:
Was the startup success rate in 2005 overall higher or was it actually due to YC selecting so well.
Also, success is relatively defined. A $50m exit might be something that gets washed away after a TechCrunch article and a few social media posts.
But that's still life-changing money for the founders. It's not changing the world writ large, but changes the world for a few people.
= Besides, there are many successes we never talk about. Wiz is worth $32B (at least Google was willing to pay that), but rarely talked about because they're a "boring" cybersecurity infrastructure company.