Because for a long time if you wanted to build a website with no money and no experience those were your only options!
JavaScript and HTML for obvious reasons. PHP because if you didn't have your own server, you couldn't run anything else (while there were free hosting providers that would host your PHP scripts).
Lisp was a thing before PHP, and software engineers did use it but it never reached the popularity of PHP. It is in the end a question of being pragmatic, which PHP and Perl are.
Also arguably the three most popular ways anyone got into programming in the last couple of decades. Something worth pondering on.