[treyd]

They literally say in the opening text crawl that replicants are genetically engineered from humans. A major theme through the movie is that they're like humans, are built to have the thoughts/emotions of humans (even if experienced in the context of implanted memories), but they can never really be humans because they're synthetic and engineered to have the traits they do and die an early death.

Robots and AI do not experience and interact with the world in a way that's comparable to humans. We don't yet have the epistemological framework to reckon with what it means to consciously experience reality in a non-biological entity, but we do know that it will be alien and unlike human cognition.

Replicants have the same biology and cognition as humans, so we can relate to them and them to us, which puts the scenario in a different context.