It seemed like so much of the web ran on it in the late 90s and early 2000s that it would have at least as much traction as PHP does today.
One can speculate what might have happened if focus had been put on evolving Perl5, or getting Rakudo production-ready as-is instead of going through yet another round of 'tinkering' (eg making the compiler backend-independent, the New Object Model refactor, creation of MoarVM, the Great List Refactor, ...) - however my crystal ball seems to be broken and just continues to display 42 no matter the question...
I don’t remember Perl losing mindshare around that time; quite the opposite.
Specifically December 25th 2015.
True, but when your reaction takes 10 years, you lost a lot of ground. When perl6 was started perl was declining but still in serious use.
It's percentage has dropped by a significant amount, but I would bet the amount of new code has not dropped nearly as much.
Also I'm fairly certain that Go is close to a 10 year reaction to Python. (If not it's implementation.) The only difference is that it wasn't done in public. It's so much easier to ignore the years of development when you can hide it.