"I spoke to many of the owners today and it is just getting too hard and too uncertain," Purdon told the Herald.
"Initially when we started talking about me taking some of what are now Hayden's horses to Australia for the best races, we would have been able to travel between Victoria and New South Wales like normal, which was crucial for them to race at both carnivals.
"But we are not sure when that will open up again and then there is the question of quarantining on the way back home for me.
"So a few of the owners are happy to leave the horses here while we have made other arrangements for those who still want to go."
New Zealand Cup winner Self Assured and Auckland Cup winner Amazing Dream, will stay home, returning south after Self Assured races at Cambridge on Friday.
They were among the favourites for the Hunter Cup, Miracle Mile, Chariots Of Fire and Ladyship Mile.
Spankem, a former Miracle Mile winner, will head to Sydney and join the Paul Fitzpatrick stable, with the intention he will be back to Cullen's care after the Miracle Mile on March 6. Ashley Locaz is likely to be flown to Victor Italian Lad may join the Craig Cross stable in Sydney.
None of Cullen's three-year-olds will head to NSW for the derbies and Oaks there.
The change of plans, while primarily caused by Covid, has still shaken up futures markets which were framed with the understanding Purdon would travel with the horses and effectively train them.
So bookies and punters will now have to get used to markets which are no longer framed with the All Stars more often than not providing automatic favourites.
Purdon and Rasmussen have taken most of this week off to give Cullen clean air as the new trainer but will drive Self Assured (Purdon) and Spanken (Rasmussen) in the Flying Mile at Cambridge.
As good as the pair are, they face a huge task because with the preferential draw they have drawn the outside two barriers while Copy That, who has beaten them both before this season, gets barrier three on Friday.
The night's other feature sees Majestic Man set to start a hot favourite in the 1700m sprint for trotters.