Sydney and Melbourne rental vacancy rates massively increased during 2020 as discussed in the following ABC News article - https://www.abc.net.au/news/2021-01-12/sydney-melbourne-rental-property-market-darwin-housing-sqm/13050748.
Further to this, see below the vacancy rates for 2020 for Sydney (2000), Melbourne (3000), and Darwin (0800) - vacancy rates in Sydney and Melbourne hit double-digits during this time, causing a massive fall in rents in apartments in the city.
This excessive supply of apartments in Sydney and Melbourne (combined with the impact of COVID) is likely to have caused this.
Darwin's low vacancy rates over this period is interesting (particularly recently, with vacancy rates at around 2%).
