I disagree on the animal comparison. Every animal created has already had all of its lines planned out, as Larian is extremely fond and acutely aware of the fact that speak with animals exists. So while it is a large task, Larian brings every animal in with the framework for it ready to go, meaning they don't have to go back and retroactively fill in as many gaps from immersion breaking circumstances.
I agree with your other examples, but from my experience those also seem far from being fully implemented. They are also extensive tasks, so that's understandable, but like I said will take time to fully flesh out.
Every situation in which silence could be useful narratively is also hand crafted, like not waking up the goblins. For things like no battle sounds, Larian can globally disable extra enemies entering combat if they can't hear it.
