Why are cane toads so successful in surviving in Australia?

If you are talking about Rugby League supporters, they have the better side.

If you are talking about the amphibians imported eighty years ago to destroy the sugar cane beetle, it is because they found a rich source of insects other than cane beetles and spread accordingly. Their proliferation should have provided good food for birds and land carnivores, however the poison glands on their back killed off potential predators who learnt to leave them alone, and so they proliferated and spread virtually unchecked by the natural food cycle which controls other creatures.

It is only now that such birds as crows have come to learn to flip them on their backs and eat their underside to avoid the poison, but this activity is so minor at present that the toads are now spreading to the western part of the continent.