PHP was a no-good, terrible, poorly-made, horrific original design for something like powering Facebook. As a result, it needed a lot of good and important improvements.
Or to be more specific, it was a great design for what it was intended to be: a pet hobby project to make it easier to make Personal Home Pages, and was never intended to be a programming language.
https://en.wikipedia.org/wiki/PHP#Early_history
The concept of putting out something this bad, and then refactoring for over a quarter-century to make it almost-usable, is exactly the definition of the webdev way.
The result is a ton of churn.