>C compatibility / extension compatibility - nope. First, it is an issue of limited resources.
No, its an issue of reinventing the wheel. Native code is native code. Numpy stuff isn't going to be faster running in pypy, neither is any of the ML stuff. Stuff like FastAPI or Uvicorn aren't going see much speed increase.
In the modern world, there is basically no need for middle ground performance. In the past, when you had single core processors, making things go fast was advantageous. Now, if you need to go fast, you most likely need to go REALLY fast, at which point just go full native. Otherwise, you are going to be slowed down by network calls and other factors.
So while PyPy is a cool projects that can be an optimization on top of regular python, its not worth while trying to make Python into something it will never be