Why did Interplay's Lord of the Rings trilogy never finish?

Interplay's plan was as clean as the books: three role-playing games, one per volume. Vol. I, adapting The Fellowship of the Ring, shipped in 1990. Vol. II: The Two Towers shipped in 1992. A third volume, Vol. III: The Return of the King, was planned for 1993, and then simply never appeared. Vol. II even holds its ending back for it: the Ring is never destroyed in the game, because those final scenes belonged to Volume III.
Here is where this page has to be straight with you. For some cancellations the record is rich: producers explain budgets, licences and studio politics on the record. For Vol. III, the record is thin. The sources for these games confirm that a third instalment was planned and never released, and that Vol. II's Amiga version was cancelled alongside it. They do not document a reason: no sales figure, no cancellation statement, no interview explaining the decision has the standing that, say, the White Council's later cancellation has.
What can be said from the record is context, not cause. The reviews were mixed rather than disastrous, and at least one major reviewer called Vol. I the best Tolkien adaptation yet made. A separate Super Nintendo line under the same Vol. I title did die for a documented reason, poor sales, in 1994, but that was a different game by the same publisher, and treating it as the PC trilogy's explanation would be inventing a fact. The trilogy did not finish, and the surviving paper trail does not say why.