Because you are more than atoms. You are a pattern. A pattern plays out over time. Like music. Music has a physical component, of course, but music is enjoyable because it's a pattern over time.
Which is the "real" Moonlight Sonata: Beethoven's original sheet music, the first performance, the photons carrying some radio broadcast, some physical vinyl or CD master copy, a lossless encoded digital copy?
The thing about a copy, it reproduces that pattern. The question is, how good does a copy need to be to retain the important features? For now, I suspect that any attempt to actually scan a brain would be a cargo-cult copy of a mind… but I don't know that for sure, I'm just going with what I hear from the occasional neuroscientist who bothers to comment on misconceptions in this field.
