Then, let me quote the back cover text:
A new, self-contained campaign arena conceived by Jeff Grubb, the ODYSSEY (TM) setting can be placed within any ADVANCED DUNGEONS & DRAGONS world. New barbarian character kits, new forms of magic, and the opportunity for new styles of role-playing make Jakandor: Island of War a fresh experience for all players, novices and veterans alike.
It was never intended to be a campaign world in its own right, but to be slotted into any other world or be run as a one-off.
Maybe TSR saw the problem with their too many worlds and tried to garner the support of fans of different settings - though how an island setting should be interesting for Dark Sun folks eludes me - maybe they were frantically testing new approaches. But at least they prominently TradeMarked the name Odyssey, hoping to start a long line of successful supplements with it.