They're either an invasive species, and therefore should not be introduced to the area (and you know that many pets will be introduced once the novelty wears of

They're either an invasive species, and therefore should not be introduced to the area (and you know that many pets will be introduced once the novelty wears off). Or they're native to the area, and should be left alone because they're endangered or otherwise threatened. Those are just two reasons, but I'd bet they cover a lot of cases.