It was so that people with GFPTs could carry on flying without doing navs and a way for people with RA Aus pilot certificates to switch to GA and fly bigger aircraft.
Also so that people who didn't want to fly in CTA could still be able to go further than 25nm as CTA is required for the PPL.
There is a lot of misinformation flying around although the rules as posted by Stretch06 are easy enough to find.