Why International Accredited Registrars?

As the title suggests, I'm a little confused as to the number of international Accredited Registrars working in the hospital system. I can somewhat understand the rationale in bringing over fully specialised IMGs (finished fellowship in their home country or abroad, and have worked as consultants) that come over - but international reg's does our own service reg's so dirty? Why snub a PGY5 anaesthetics keen domestic graduate only to have to go and fully train an international reg???

Am I missing something?