Because ISO languages are usually designed on paper, with some of the features being done on whatever compiler the respective paper author feels like, thus compilers only rush out to fully support a new standard when it gets officially supported.
With Python, there is no standard per se, it is whatever CPython does, and everyone else has to try to mimic CPython.
With Python, there is no standard per se, it is whatever CPython does, and everyone else has to try to mimic CPython.