The answer is simple—Python changes because there is such a need. The competition does not sleep. Every few months, a new language pops out, out of nowhere, claiming to solve every problem of all its predecessors. Most projects like these lose the developers' attention very shortly, and their popularity is often driven by sudden hype.
This is a sign of some bigger problem. People design new languages because they find that existing ones do not solve their problems in the best way possible. It would be silly to not recognize such a need. Also, more and more widespread usage of Python shows that it could, and should, be improved on in many places.
Many improvements in Python are driven by the needs of particular fields where it is being used. The most significant one is web development. Thanks to the ever-increasing demand for speed and performance...
