King's Knight looked like a Zelda-style game, it was not. It looked awesome, it was not. King's Knight was a forced-scrolling shooter with terrible jumping thrown in. Most of the game play was getting crushed by terrain at the bottom of the screen. While I have no data, my guess is that after the release of Final Fantasy, a lot of very confused kids bought this piece of junk.
Now in an attempt to rehabilitate Final Fantasy, which has had a rough decade, Square Enix is tying the return of King's Knight to the upcoming Final Fantasy 15.