More that the hyper-efficient food supply chains of modern supermarkets demand rigourous reliability, which industrialised growing and slaughtering of cows, pigs and chickens can provide, but hunting kangaroos cannot.
I also suspect that when considering transportation costs, chicken farming is probably more energy efficient than industrialised kangaroo farming. If Australia had a more developed hunting community, it would provide a good protein source for rural/regional communities though - like deer and boar do in the USA.
Why not introduce Kangaroos into the wild in the USA or other landmasses, if they are ecologically efficient?