It's about participation.
Many players, including myself, play footy until the end of high school or early uni, but then participation drops off steeply. It's much easier to play sports like basketball or 5-a-side soccer on a weeknight evening with a few mates, than set aside a day on the weekend (plus two nights of training during the week) to play organised footy.
The AFL has tried a few things like AFL 9s, but they haven’t taken off. I reckon this is their next attempt, and they’ve figured out you won’t get people playing unless you are exposed to the form of the game in some capacity. Hence shoving it down our throats in September.
Watching it will probably be rubbish, but a short version of the game to play is a good idea.