Why would trump impose tariffs on uninhabited islands?

"Among the locations Donald Trump slapped with tariffs Wednesday are two uninhabited islands near Antarctica in the southern Indian Ocean.

The Heard and McDonald Islands, which sit about halfway between Australia and South Africa and are territories of the former country, now face 10 percent tariffs, which would pose an issue if the seals and penguins that call the small landmass home were exporting anything to the U.S."