That'd be because, like Australia, there's a very isolated ecosystem there that could be decimated by unintentionally bringing in diseased fruit from overseas.

That'd be because, like Australia, there's a very isolated ecosystem there that could be decimated by unintentionally bringing in diseased fruit from overseas. Australia has similarly strict rules on bringing food items, etc. in because it has a similarly isolated ecosystem where some diseases prevalent elsewhere simply aren't found here, so the ecosystem isn't resistant to it.