Well not just what they know, but what all their existing stuff is written in. Makes sense too. The two Perls aren't really that compatible, far worse than migrating Python 2 to 3 and companies struggled with that manoeuvre. You can run and call each language from the other, with some in memory wrangling between https://github.com/niner/Inline-Perl5 But the same is true for Python and Java objects.