Artificial intelligence is hard. Why reinvent the wheel, when you've got plenty of humans walking around? Who will miss one, right? Alternatively, you might be one of those humans looking for easy Immortality. Either way, once you finish scanning the brain, you end up with a file that you run in a physics simulator, and presto, you have a computer that remembers being a human. If you do it carefully enough, the original brain won't even notice it happening. There's also a pile of legal, moral, and theological questions that might be addressed in the story: