I’ve been using PHP for over a decade and have never used FPM.

“Using a single language for both frontend and backend with (largely) the same availability of tooling and the ability to share code”

Is a negative I went backend world and front end world to be different because they do very very different things.

“But more than that... it's just less used? The PHP ecosystem is noticeably smaller and has way less happening.”

That’s not true, PHP is less resume driven development and actually about productivity. I’m really happy narcissist hate PHP and don’t burden it with their garbage and slopworks.