New versions of perl get released, and the code doesn't work with it.

New/old operating systems acquire a perl, or a user, and the code isn't portable to those systems.

Bug reports accumulate, feature requests accumulate, doc requests accumulate; the whole lot get swamped in an undifferentiated morass of duplicates and near-duplicates; the module gets a bad name and falls into disuse.

None of these necessarily affect a working program on a single machine on which nothing changes, but few machines never change. Likewise, though the code doesn't change people's perception does, and I'd rate it unwise to choose to use an unmaintained module for new code for anything but a one-off run-and-discard script.

Hugo