Way back, Perl got off the ground really because, in contrast to the C compilers of the era, code written on one Unix ran on the others, usually unmodified. In my first jobs, where we had heterogeneous mixes of commercial Unixes, this was unbeatable. It also wrote like higher level shell, which made it easy to learn for systems people, who really were the only ones that cared about running things on multiple platforms most of the time anyway.
As things became more homogeneous, and furthermore as other languages also could do that “one weird trick” of cross platform support, the shortcomings of both Perl and its community came to the fore.