Alot of illegally imported organism's are destroyed in customs due to either them contaminating the destination, or contaminating/getting contaminated by shipping them back to the country of origin.
Imagine sending them back to the native habitat with all sorts of non native parasites.
Or importing a species that is known to harbor a deadly parasite, even if its going fro customs directly to a isolation unit.
Hell you cant bring home a coconut from the bahamas to Florida for the same reason.