To me it sounds like a measurment problem first. For instance many Boomers are obsessed with the Beatles or The Rolling Stones and probably listened to their albums a lot more than a local band such as Cream, but the the listens weren't measured only the sale was.

charts used to be based on purchases of records, CDs and cassettes, they now include digital downloads and streaming, which account for more than 70% of industry revenues. Streaming has risen more than 50% in Australia in the last five years but the share of streams that are Australian content has fallen 31% over the same period

This 31% number seems to be the closest the article comes to explaining why there may be a meaningful drop in interest in Australian music. But it doesn't develop that part enough.

The Ol’ Gizz and the Psychedelic Porn Crumpets have never rocked harder

I wonder what percentage of the population is listening to "top 100" now vs 30 years ago.

In the age of streaming and algorithms the shared culture is not the same. Tastes are much more fragmented.