Why do queries for NSEC3 records fail to return the NSEC3 record?

AA-00289

Although NSEC3 records are present as part of a signed DNS zone's representation (in master files and zone transfers), they are strictly metadata and cannot be queried for directly. The owner names of NSEC3 records do not form a part of the DNS domain tree. Signing a zone using NSEC3 records does not bring names into existence that do not exist in the unsigned version of the zone.

NSEC3 records are only returned in the authority section of  negative replies to DNS queries (negative replies such as NXDOMAIN and NODATA - see RFC 2308) and are used specially in validating the proof of non-existence.