Talk:My Little Pony Equestria Girls: Friendship Games/@comment-24981516-20150818050611/@comment-10390252-20150818120547

Because the Sirens were magically exiled to the pseudo-human world more than a thousand years ago by Starswirl. The portal is the logical means by which he did it. I would doubt any other mage with the exception of Twilight Sparkle has ever been strong or wise enough to craft such an artefact.