Because Guido van Rossum just isn't very good with performance, and when others tried to contribute improvements, he started heckling their talk because he thought they were “condescending”: https://lwn.net/Articles/754163/ And by this time, we've come to the point where the Python extension API is as good as set in stone.

Note that all of the given benchmarks are microbenchmarks; the gains in 3.11 are _much_ less pronounced on larger systems like web frameworks.