Why does JCU require a Data Record and Data Publication (in Research Data JCU) if I’m publishing through an external data repository such as GenBank, PANGAEA?

You are still required to complete these records in Research Data JCU. 

A Data Record helps researchers (and JCU) keep track of data associated with their projects including the location of data held in other trusted, often subject-specific repositories such as GenBank, PANGAEA etc.

A Data Publication is a public metadata record and assists researchers to increase the visibility of their work. These records are harvested (uploaded) by Research Data Australia and other services which allows other researchers to find datasets for future research, collaboration or reuse.

Note: JCU also holds Data Publications for data held on repositories such as Dryad. However, because JCU is not the primary publisher, DOIs are not minted for these datasets as they usually already have a DOI and having multiple DOIs dilutes any altmetrics etc.)