Because the value of a digital record depends as much on how it was obtained and kept as on what it says. If you cannot document who took the data, when, and by what method, the other side will argue that the record may have been altered afterwards or obtained unlawfully — and the evidence becomes something to litigate about rather than something to rely on.
The chain of custody is the unbroken record that closes that gap: forensic imaging, integrity verified by hash value, access logs and every step committed to a minute. Kept properly it answers objections to both the integrity and the lawfulness of the evidence — under the Code of Civil Procedure (No. 6100) in civil proceedings, and the Criminal Procedure Code (No. 5271) in criminal ones. That is why we build the chain at the very beginning, when the first copy is taken, and keep the finding defensible from there.
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