It's ultimately supply and demand. We have enough pilots but the supply says 'we don't want to move to PER'.
Well what's stopping them from advertising for and recruiting directly for 737 FO? Perth Base? Surely that can be done if people are needed in that job but no one in the company wants to do it?
It makes so much more sense than selecting people for one job and then on day one of recruitment asking them if they'd like to take a different one.