Intended use case is for relay access control and user trust scores. That's a pretty desireable use case regardless of how other clients implement it.
Discussion
So paying for more NIP-05s means more trust?
We can give NIP5s away to whomever for all it matters. That's not the point. It's how they get used in a trust relationship. It is simply easier for a relay operator to whitelist a nip5 domain at scale than it is to manage each individual npub.