Let $A,B$ two questions and suppose $B$ is a duplicate of $A$. Then (usually) $B$ is closed and a link to question $A$ appears in $B$. However, it may happens that $B$ already got a useful answer which is also different (or better explained) from the answers proposed in $A$ (see for example here or here). A copy-past of the answers proposed in $B$ in the answers of $A$ is clearly not always possible since the notations introduced by the OPs may be different.
My question: Why isn't there any path from $A$ to $B$ when question $B$ is closed as a duplicate of question $A$?
This would make sense to me because then the OP of $B$ would have access to ALL the answers to his question. For example, if $A,B,C$ are questions such that $B$ and $C$ are duplicates of $A$ and there is in $C$ an answer that would help the OP of $B$ more than the answers proposed in $A$.