[Sniffnoy]

An interesting post I read recently about why we haven't: https://svpow.com/2024/09/07/were-not-going-to-run-out-of-ne...

Of course, that's specifically about human anatomy. In this case we're talking about a feature that I'd bet is present in other animals too, so the factors discussed here don't all apply. In this case though there seems to be a straightforward answer -- the structures involved are very small! The post I linked is largely talking about larger structures we failed to find...