The entire reason PHP grew so wildly in popularity was because hosting providers made it so you could just FTP a file with a .php extension to a server and it ran. Apache was the default web server for shared providers because you could do per account config like url rewriting by uploading a .htaccess file. Virtually no one was configuring their own servers or installing Linux on bare metal for websites.

That was a big reason, but I think another key choice was that the output format (HTML) and the input format (PHP) could be pretty close. If you were 15 and wanting to make a dynamic webpage, you'd look at an existing web page, copy it, and change one bit. PHP made that easy. The next change and the change after that were easy too.

In contrast, competing technologies started out with, "OK, learn computer science. Now learn how HTTP works. And then learn CGI. And some Unix. And then you can do 'Hello, World.'"

The funny part for me is that a lot of us in the latter camp didn't learn computers that way at all. We started out with BASIC:

    10 PRINT "Onion2K is cool!"
    20 GOTO 10

It had the same immediacy as PHP. The ease of making something happen was what drew us in. But somehow we forgot that. While also saying, "Here's something that will touch everybody on the planet. Let's all use it!"

Not just for websites, for other stuff.

How many people had rented servers for games? A lot. Now video game companies have turned game servers into a SaaS, whereas then they just released Linux server binaries. In the early 2000s there was a bare metal server rental company on every other street corner.

How many people had Linux/BSD network appliances? Also a lot. There was such a time when all you got from the cable or telco for your broadband service was a modem, and you had to roll your own router/switch. There were a multitude of run-from-a-floppy (or USB stick) BSD and Linux router distros back then.

Also, you're not correct on PHP. The entire reason PHP grew so wildly was because it was server side rendered, and both AOL and Microsoft intentionally hindered their browsers' javascript capabilities in lame attempts to monopolize the internet.