It might make sense to temporarily exclude a package from installation if the available version is known to be buggy, though this would rarely occur on a server where one generally installs distributions that don't update often except for bug fixes.
A reason that comes to mind for excluding perl specifically is if there is a separate installation of perl, possibly directly from CPAN, possibly shared or synchronized with other machines on the network to ensure consistent sets of installed libraries and versions. Look in
opt for an alternate perl installation, check for a
PERL5LIB setting in
/etc/profile. I wouldn't do it that way, because as you noticed it will break dependencies, but I can see why someone might be tempted.
Maybe if you post the full set of exclusions someone will spot a pattern. Is there any comment in the file that might give a hint?
To avoid this kind of issue in the future, you should put all configurations under version control. Then the changelog would indicate when the surprising configuration was set up, and hopefully why.
On Debian/Ubuntu I use etckeeper, which I think has been packaged for CentOS too. On a multi-administrator machine, it should be set up never to commit changes automatically, forcing the administrator to make an explicit commit before they can run
yum install or