In 2011, around 47% of the Australian population had a parent born overseas. It was about 27% themselves born overseas (roughly 40-50% from Asia/Africa — is Oceania part of Asia?) and 20% who had a parent born overseas (struggling to find distribution for this).
Maybe it’s just a money thing — do Cat Bs count in the normal salary cap? — but I find it hard to believe clubs can’t find legit candidates.
Cat B's don't count in the normal salary cap, and I'm pretty sure Oceania isn't Asia as far as the AFL is concerned. As for the other part, that's the theoretical purpose of the next generation academies; those are the demographics with lower participation rates in aussie rules.
The other factors for me are the reality of the available pool, and the AFL being stupid. On the first, even if participation rates across the demographics were equal, you're looking at 15-20% of the available players who weren't in the top 130 available players, so it's always going to be a reach. On the second, the AFL announced the initiative in late July this year which isn't a lot of time to change approaches and dedicate some resources to scouting those players.
I'm still kind of surprised more clubs didn't take up the option, because it is a free hit, but the AFL basically sent the idea out to die in the first place.