That's... not quite true. There are actually dozens of arrangements of FFMQ out there, just none of them are ever submitted to OCR for whatever reason. Here's everything I have from my personal collection: http://kngi.org/private/miscstuff/ffmq/ (note that I cannot vouch for the quality of this stuff. Your mileage may vary.)
Also, there's this: http://danieltidwell.bandcamp.com/album/the-mystic-quest-for-metal-a-tribute-to-the-music-of-final-fantasy-mystic-quest
And this, which is a joke album (so again, your mileage may vary): http://ffmq.olremix.org/
By the way, this is the ELEVENTH thread posted here dedicated to FFMQ. I thought everyone hated the game because it wasn't a "real" Final Fantasy, but apparently not!