As one obvious example, evolution is not agentic but still answers "why" questions.

"Why do we have a heart" "Why do we sweat", etc.

But Chesterton's fence is often used in an even MORE generalized way than just that, not "why is it there" but "what are we not seeing about how this connects to everything else"

As an example, eradicating mosquitos. We see many obvious reasons why it might be good, we can even see that they don't seem that important in the food chain, but it would be hubris to assume we understand every potential connection they have to world ecology.