He lost his Mum recently didn't he? Maybe it has changed his perspective on things and he just needs to get away while still young.
Best of luck to him though. Big loss to the Tahs and Australian Rugby.
I was thinking something similar maybe he just wanted to get away from Sydney and Australia for a few years to get away from the constant pressure and scrutiny. Going to Ireland and playing without the stress or expectation of leading the pack or gunning for Wallaby selection will do him good.