This is a very bizzare post. Lets clear a few things up.
1) Victoria is in a massive hole ... their stakes have been slashed across the board - from the top races to the bottom and series like Vicbred and the Breeders Crown. So much so that the big rumour going around is that E Stewart is in fact giving strong consideration to setting up in New Zealand. The irony here is betting and participation at the stakes level has probably plateaued because of her dominance.
2) Moving from Victoria to Tasmania is nothing like Christchurch to Pukekohe. Yes, it will be smaller fields and less racing, but M & N Purdon don't really race on grass anyway. But the stakes are in fact better in Auckland and there are a glut of feature races, especially through Autumn, when all the open class racing is concentrated here. Tasmania has next to no feature racing.
3) Why would they want to stay with "better racing and bigger fields"?? Surely, if you operate a business, you want to go where the best yields are for you and your clients?
On a side note, I do agree moving specifically to Pukekohe is a bit weird because that track is up for sale so they are only going to have to move again within a few years.