Ratings tell the most important story that people forget; it's not about the teams so much as the storyline going into it.
Origin always rates well because the storyline, no matter who's actually on the team, is always Queensland vs New South Wales.
The 2018 NRL Grand Final rated well because it was Sydney vs Melbourne, doesn't matter that Easts are limited in terms of how much of Sydney they actually represent, the big storyline was a tale of two cities. Same whenever Melbourne go up against a Sydney side, it's easily marketed as a battle of the cities.
When it's Brisbane vs a Sydney side, it's basically mini-Origin. When it was Cowboys/Brisbane, it was huge because both teams were made up of a ton of Queensland Origin players and it capped off that period of Queensland dominance with an almost Origin vs Origin team set up.
It's also true with the AFL, the games that rate highly are always a Melbourne based team vs a WA or SA team or the Swans. Collingwood vs West Coast worked because you've got an established historical club with huge support but also huge levels of hate from other fans, vs the most successful expansion side that has about 2/3rds of a State in support and similarly huge hate from others around the country and their own state. A storyline dream, compared to this years one of established club vs expansion team nobody likes.
Canberra vs Easts unfortunately, had an interesting storyline, but it doesn't come with that same aggression that you get when it's City vs City or unstoppable force (Brisbane/Melbourne) vs gritty underdog (Sharks/Cowboys).