To be fair to koalas they were perfectly evolved for their niche and quite successful and plentiful before we came in and radically altered their environment. They suffer from the same problem as a lot of native Australian and NZ animals - over the millennia they became hyper-specialized for an environment with no agriculture, few predators and limited contact with humans. Ground dwelling flightless birds, to take another example, are well adapted to a life of foraging on the forest floor, but it takes the introduction of a handful of rats or feral cats to wipe out the species.

Whereas pandas, it seems, have always been very rare. We have ancient Chinese drawings of all sorts of animals that are native to China.. even non-native animals like lions and elephants, but there are no surviving depictions of pandas.. They were bears - fully adapted carnivores with the muscle mass, claws, teeth and digestive system for meat eating, who for some reason decided to go vegan.