They must have been cheap actresses
The very well-known Ray Meagher (who plays Alf in Home and Away) appeared as Geoff Butler, the guy who blew up Jim Fletcher's wife and kids and was then shot, before reappearing years later as a mafia boss called Kurt, before making a final appearance about 200 episodes later as the evil Governor of Blackmoor, Craven!
These were quite important parts, and he was a well-known actor - can you imagine if, for example, Michelle Collins reappeared in Eastenders in a couple of years playing someone else? Or Ken Morley turned up again in Corrie as someone other than Reg Holdsworth?
Seems the Aussies were much more amenable to saying old favourites from the acting pool reappear, whoever they were playing