Perl's decline was cultural

I think a big part is does someone starting to program even hear that Perl exists? No, and they start learning python and so have little need to learn Perl after that

That's why it has stayed dead. But that can't explain how it died. People don't just spontaneously stop hearing about the existence of a programming language in common use.

Which is (sadly) hilarious because that was the reason most people seem to have gone with python: they were told "this is what we use here" or they bought the "line noise" nonsense. They never put much effort into this.

But I also think that people who are truly interested in programming immediately learn that there are many different paradigms. And the net makes it dead easy for them to explore different directions and, I don't know, fall in love with haskell or something. Perl is plenty visible enough for THAT. I don't know about perl 6 / raku though.

How did vbscript die? How did php die? Better alternatives came along and sucked up the oxygen.