1. failing to have a coherent path to Perl 6
2. Ruby (on Rails) taking over the workhorse task of serving up dynamic content that Perl had owned before then
3. Python completely dominating the utilitarian scripting/programming world in nearly every niche
Why did this happen? I was a work-a-day developer working in Perl v5 when this transition occurred and from my perspective and recollection v6's meandering development cycle -- which didn't really address the issues of the broader Perl community was the primary choice. Perl 6 was developed in a way that didn't address the broad concerns of the Perl community, and expected people to make a wholesale switch to what was effectively an entirely new language anyways. It forced people to go out looking and what they found were either stronger solutions to specific domains (Ruby on Rails) or a nicer language than what was being proposed (Python).
Where Python really excelled at the time was that it looked and worked very much like the pseudocode that was going around at the time, and had an opinion about how you should write your code. Perl is wonderful to write in, but in many ways is too expressive and permissive and it resulted in an ungodly mess that could be hard to maintain. Perl 6 simply leaned into that problem rather than encouraging a cleaner approach.
I never liked Python much, but damn if I couldn't argue that I was much more productive with it than Perl in the end. Which was weird because when I was really hacking in Perl I could write code almost as fast as I could think giving a kind of illusion of productivity. But Python was easier to integrate into a coherent team development structure and actual productivity is more important than feels.
I miss working in Perl. But I knew it was really finally dead when I was giving tutorial classes to new bioinformaticists who were being given old Perl codebases to update and they were getting through school without learning the language.
Python was indeed the scripting replacement. I would say it won because of its philosophy on simplicity and explicitness. Perl v5 suffered heavily in complex projects because the language itself was too complex and often cryptic
PHP kicked Perl's butt in the shared web-hosting environment.
You could do amazing stuff with mod_perl, but it was not possible to run a shared host with mod_perl without exposing every customer to every other customer's code. You could still do cool stuff with vanilla CGIs. Perl was practically synonymous with CGI back in the day. Once you grew past what a simple CGI would handle, it suddenly got a lot harder and a lot more expensive.
Meanwhile, PHP had simple Perl-like syntax and ran nicely in shared hosting. Better yet, you didn't have to choose from one of the 400 different Perl templating systems. No need to choose between TemplateToolkit, HTML::Mason, or Embperl. You just used the standard, built in templating.
PHP won because it was worse, you didn't have the power or choice Perl provided, but it was more than good enough and it was cheaper to grow with.
On Perl vs Python: - Perl was weird and proud of it, it promised creative power and flexibility - Python promised regularity and clear rules
- Perl tried to make hard things easy - Python tried to make routine things routine
- Perl had weird primitives that let you build whatever magical OO nonsense you wanted. - Python supported writing glorified struct OO that was fashionable at the time
- Perl was difficult to integrate with C libraries - Pyton integrated much more easily with C libraries
That being said, I like Perl much more than Python. Using Perl still feels magical, even if some of the syntax is odd. Using Python feels like I have my shoes on the wrong feet.