It is "core" because it comes with the perl distribution. People tend to (sometimes mistakedly, I have found!) trust those modules as more stable and reliable than the modules that are only found on CPAN. Why is it in the core if shouldn't be used in production? I don't know, but my guess is that it was a response to all the people who complain that Perl doesn't have a switch statement.
Re^3: Responsibilities of a module author
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