The enormous reason that I see is the insistence, from Larry Wall and others, on a bottom-up "community" transition from Perl 5 to Perl 6. The design process for Perl 6 was announced at a Perl conference in 2000 [1]; 15 years later, almost every Perl user was still using Perl 5. The inability of the Perl community to push forward collectively in a timely way should be taken by every other language community as a cautionary tale.
Tim O'Reilly made a secondary point that may also be important. For a long time, Perl books were O'Reilly's biggest sellers. But the authors of those titles didn't act on his suggestion that they write a "Perl for the Web" book (really a Perl-for-CGI book). Books like that eventually came, but the refusal of leading authors to write such a book may have made it easier for PHP to get a foothold.
[1] https://en.wikipedia.org/wiki/Raku_(programming_language)#Hi...
> The inability of the Perl community to push forward collectively in a timely way should be taken by every other language community as a cautionary tale.
I think this is a good point that I hadn't considered before.
I think Perl stopped being able to attract new users. There is always going to be users leaving. If they aren't replaced, you will slowly shrink.
I think the point you raised is part of why they couldn't attract new users. I also think people asked themselves "why chose perl now, if I know I need to re-write when Perl6 comes?" and decided Perl5 was bad choice. I also think the fact Perl had this reputation for being ugly, difficult, and "write only line noise" kept people from even considering it, even if that reputation didn't match production codebases.
Something more niche is that I also enjoy the mouse buttons above the trackpad, I can move with the thumb and click with a finger.
This logic is why I like the tiny arrow keys. I find it pretty easy to move my pinky over and tap one of those keys. With full size keys, I find that doesn't really work.