Well, they did at one point, seeing as one of the previous Empress' was a love interest of the King of the original Kohanians. Plus the fact that Yui nearly died on the planet to Shadow, and was saved by Gnarlpaw, the current Avatar.
On a side note, Five, was that really a comment that needed to be made?
And on a sidenote on the other side of the page, I just meant that if the Kohanians were to be mentioned, there would be a lot of tropes that we might not want to be attributed with.