How has SoO become such a massive thing

Because fuck Queensland, that's why. More seriously, compare it a little to the Ashes - in the begin the much less fancied QLD got an upset, NSW sought revenge and so on. The players show way more passion in it than in any club game, even in the early days which made it easy for fans to get behind. Add to that how close and competitive it is every year (even when QLD won 8 straight, the individual series were tight, only one was 3-0). Over 30 years its just swollen in importance fairly naturally as the title switches hands in close contests, and add that for most of that period both teams have been better than either NZ and England, making it the highest quality form of the game (though not at the moment because the Kiwis are better than the Roos).

How can AFL do it successfully? Hard to say because it would be a tri-series. Victoria getting humiliated early on in the competitions life would certainly help, I would expect SA and WA would have a greater level of passion there to begin with wanting to get one over them, but within a few years the Vics have to want it too for the competition to succeed. You can't really do anything ensure it will be a close contest, but if one of the three is getting smashed constantly that'll stop it becoming big, and someone is always going to have to miss out if there is a final, which makes things difficult.

I think a NSW-QLD Origin series would be a great way to get people here to get into AFL, though. The culture is already there, so much so that people get hyped up for Origin in weird shit like water polo and woodchopping. Run it alongside the 1st tier Vic/SA/WA competition and it'd be good for time zones. The Swans are the punchline to jokes, but by god you give us the chance to smash the Toads in some new sport and people will get behind that shit.