Subscriber numbers are the fundamental factor as to whether or not a streaming service lives or dies.
And if you don't have the big content carrots to attract subscribers, you don't have a service. Sport and branded IP content are big carrots. AFL and NRL are big carrots. And yes if you're talking about the size of the carrot, then by viewer numbers, yes the NRL carrot is larger. But that's not to say that AFL isn't a big carrot too. It's unwise to think that.
As to runtime, in 1995 on FTA the AFL's 3 hour run time made it a powerhouse. But what was it competing against? Burke's Backyard? But now there's a plethora of entertainment options and people's attention spans are getting shorter. Every show is competing against a billion websites and apps. Do you realise how hard it is for adults to commit to 3 hours of viewing, let alone teenagers? You'd better have something with 10,000 superheroes in it and the whole universe is at stake. Half of you are probably reading this on your phone or tablet whilst you ignore the television in the background.
The NRL's shorter game time is actually to its advantage. People are more likely to tune in for 2 hours than 3. And the people who do watch multiple games know a dud game in the NRL might be only 1 hour away from the next better one. But in AFL it might be 2 hours. The NRL can also show multiple games back to back in prime time when most viewers are watching, particularly in the 6-10pm peak times. That's literally Friday night football right now. Where's as it's hard to do that in the AFL.