Perl's decline was cultural

Perl grew amongst a reactionary community with conservative values, which prevented it from evolving into a mature general purpose language ecosystem.
. (This is a drawback about fort-building. Once you live in a fort, it’s slightly too easy to develop a siege mentality).
if difficulty itself becomes a badge of honour, you’ve created a trap: anything that makes the system more approachable starts to feel like it’s cheapening what you achieved
Perl had an, at best grudging, tolerance for ‘difficult genius’ types, alongside this baseline culture. Unfortunately, this kind of toxic personality tends to thrive in the type of culture I’ve described, and they do set to help the tone.
If Perl can already do anything, flexibly, in multiple ways, then the language itself doesn’t need to change - ‘we already have one of those here, we don’t need new things’.
If I squint, I can imagine that a Perl with a less reactionary culture, and a healthier acceptance of other ideas and environmental change might have been able to evolve alongside the other tools in the web paradigm shift, and still occupy a more central position in today’s development landscape.