It's still used because momentum is a powerful factor. That doesn't make PHP better, but it can make it a more expedient choice.

PHP is a preprocessor that grew too big for its britches. It's a monolithic monster that runs only one thread per request in an interpreter. It works well enough if you need to manage the data of an internet forum, but it becomes increasingly unsuitable as the task's complexity grows. If you need threading or background tasks, or if scalability is important, PHP is not it; just read any number of Nextcloud vs OpenCloud comparisons.