Unfortunately this has led to kangaroos reaching plague proportions. They destroy farms, tear down fences and generally be a nuisance. You can barely drive through rural roads without breaking a sweat in case a kangaroo jumps in the way of your car.
The problem here is multi-fold.
The location issue:-
1. Due to Australia's sharp weather, areas could suddenly fall under drought which would result in a sharp decline in kangaroo numbers.
2. As a result of this, kangaroo culling is disincentivized in other areas even though there is an uptick rather than a decline.
The species issue:-
1. There were originally about eight distinct breeds or so of kangaroo, but things like hunting and drought has reduced the numbers of those species dramatically.
2. The outcome was to limit the amount of kangaroo culling so as to not affect other breeds.
3. As a result, overall numbers haven't declined - rather they have sharply risen - and certain breeds have "muscled out" the at-risk breeds.
Firearms laws in Australia:-
1. The Australian government banned most firearms after a massacre in 1996.
2. The Australian public has since come to find guns "dirty" and Australian lawmakers (coincidentally, those belonging to the same parties that outlawed hunting of kangaroos) do not want to promote firearms (even in a licensed, limited fashion)
3. Promoting the culling of these species would run counter to their political discourse for the last couple of decades.