Because of population. It's basically this but comparing USA and Canada and showing it as a bar chart.

They are apex predators in Australia. There are no large carnivors that take them out. Dingoes are not common, a cat would give a Goanna a run for its money, cats don't go in the water so sharks are a different environment, crocodiles live in a small portion of the country. A cat will hunt snakes, snakes will typically only defend, but not all snakes are poisonous and cats have been known to win against the poisonous ones. Wedge tailed eagles again are not everywhere and are mostly just scavengers. Emus are fucking idiots.

When cats get out here they go feral and eat everything in the immediate area. The feral cats that have been feral for generations are significantly bigger and more aggressive than a house cat, and will actively attack sheep.

They are in New Zealand, where the problem is worse than in Australia. New Zealand has zero native land predators. There are some birds of prey that can hunt invasive stoats and rats, but cats are effectively uncontested (with the exception of humans performing population control).