Random pedantry: the list on that page is the stuff where people have typed `brew install perl` (or `brew upgrade perl`) and it hasn't been pulled in as a dependency. As to why: I have no idea :D
I have no data to back this up other than my anecdotal personal experience but I'd wager Perl hackers who use Homebrew never use it to install Perl.
Most of the classic Perl documentation walks you through installing from source, which is quite easy, and modern documentation/tutorials usually refer to perlbrew.
The Perl community often has established solutions within their own ecosystem, and this makes them seem like they have a smaller presence then the otherwise would have.
Also, Perlbrew is not necessarily easier, simply because having one package manager manage your packages is better than having many package managers (cargo, npm, gem, etc). It suggests that maybe there should be a package manager for all these package managers... I'd personally want to use the simplest way possible to install something unless I had a reason.