DKIM is not meant to block spam, it's meant to authenticate that the sender had access to the private key for the public key exposed on the domain that it was sent from, implying that the sender has sufficient permissions to send from the domain.
It should not be used to imply anything else, none of these have anything to do with spam, that's reputation (and yes, having DKIM set-up boosts your reputation but it is not sufficient) and should be "built" up by the domains sending the emails.