Only because the studio made Ridley Scott cut the scene. Ridley Scott definitely thinks Deckard is a replicant and interviews of him show that it was his intent

Only because the studio made Ridley Scott cut the scene. Ridley Scott definitely thinks Deckard is a replicant and interviews of him show that it was his intent. On the other hand, the book says Deckard is a human. So it depends on whether you prefer Ridley’s version or the original book’s version, but it wasn’t supposed to ambiguous.