The problem comes when deploying PHP to someone elses server. Since apache and PHP are usually tightly coupled together and PHP has a concept of global configuration that applies across the whole server.

So you have some PHP app that works fine locally but fails in weird ways on deployment because the server was configured using cPanel by someone who didn't know what they were doing and if you change settings you risk breaking whatever other random php scripts are running on the server. So you end up hacking around with .htaccess files to get things working.

With Django etc you get a to have a "clean room" and run in relative isolation, only interacting with the outside world via proxies.

What PHP is however is cheap to deploy. It's annoying to have to think about and pay for "instances" , "dynos" , "VPS" etc when you just want to put up a webpage with a bit of server side logic.