Plainly Kerry Packer didn't get all the exclusive television rights he wanted. For some years after, Nine had the capital city rights to test cricket while the ABC retained the rights in the rest of Australia.
Aggregation pretty much spelled the end of ABC's involvement in Test cricket as the eastern states all became covered by Nine affiliates. I seem to recall the ABC's commentators did acknowledge the day of their last Test cricket coverage which I guess was 31 December 1991 as Victoria and NNSW were being changed over in aggregation as their respective Nine affiliates took over from 2 January 1992.
And to all those people whinging on Twitter about the amount of ads played during the program... umm, yeah, that's how commercial TV is made. If you want less ads go and watch The Shire
that's how cheap TV is made.
And while I'm not always one to nitpick about historical anomalies in these things... although sometimes it is fun, and because I accept it's not strictly a documentary... but it looked like Nine used a more modern variant of their dotted logo rather than the 1970s original which would have been in use at that time. It looked like the Nine logo depicted was a more modern version that was adopted around the time of digital, which had the "9" presented in a slightly thinner type and the dots more widely spaced, while the original was thicker, bolder type.