Humans are also pretty notoriously bad at doing this. It's also very easy to be inspired by something then forget the source. Humans often perform reverse-attribution, where they later realize or someone else points out a similarity, and only then do they add the citation.
Granted. This is why we built a rather complex set of rules and enforced habits around this and, if there's any doubt, rather dismiss a given production not adhering to these rules.
