Because you can only see well with the heart. Of your enemy. After you ripped it out of his chest.
Which is why the Klingon Version of the Little Prince is now available on Earth.
Or at least in some parts of Earth. It’s a project by a German, hence the only available subtitles in the Promo Video and I can’t tell if your local Amazon delivers... ;)
Then again, for many Americans the difference between Klingon and German seems only marginal, awnyway I guess.... :)