Prior to the development of a livestock industry, vast areas of Australia were once without drinking water for a majority of the time. Today, thanks to bores and dams, most areas of Australia are less than 8 km from water - an easy hop for a kangaroo. Where there is drinking water, kangaroos thrive until they starve. Death through starvation is a slow and painful affair. If dingoes were still widely spread they might control kangaroo populations but the dingo has been exterminated from most areas except central and northern Australia.
Kangaroos have two long, soft feet.
Sheep, cattle and goats all have four hard hooves that chip away at the soil. Regardless of what sort of feet they have, one kangaroo or one sheep has a negligible impact in a 1000 ha paddock. However, a hundred kangaroos or a hundred sheep can equally damage a landscape. It's the total number tearing away at vegetation, exposing it to erosion by wind and water that matters. When there are a lot of grazing mouths, the land is at risk of falling apart.