[urlhttps://www.nrl.com/news/2018/11/05/why-kangaroos-tour-is-best-chance-for-australia-england-showdown/[/url
Given the GB tests down under won't feature Australia (apparently), it looks like the Aussies want to head north next year with midweek games v Ireland, Scotland, Wales and France.
Personally I see this as the getting a chance to build their squad for the RLWC 2021 by bringing down 2 sides and getting more experience for their side that now needs to find a new spine.

I thought they agreed to tour in 2020 when the RFL said it would be better to build momentum going into the World Cup?

They did, but rumours coming out of Aussie seem to point as the Aussies not wanting to play GB next year and as much as Playing Tonga and NZ in Auckland will be great (for me especially) I don't see the GB brand as anything other than an ashes tour.....