the reason PHP is so popular is because it's easy to lock down for a webhost that wants to isolate its users from each other
What the hell are you talking about? How does PHP help to isolate users from each other? You seem to have PHP confused with a security-minded programming language. You must not have gotten the memo.
Also, PHP is popular because it was the first HTML template language with a programming language built in, at a time when Perl, the then de-facto language for web programming, didn't have any decent template libraries.
You obviously weren't programming in the 90s, so please stop trying to rewrite history like you were there or have any idea what was going on.