I can think of two possible reasons:

First is the Google's manpower. Google somehow succeeds in writing fast software. Most Google products I use are fast in contrast to the rest of the ecosystem. It's possible that Google simply did a better job.

The second is CPython legacy. There are faster implementations of Python that completely implement the API (PyPy comes to mind), but there's a huge ecosystem of C extensions written with CPython bindings, which make it virtually impossible to break compatibility. It is possible that this legacy prevents many possible optimizations. On the other hand, V8 only needs to keep compatibility on code-level, which allows them to practically switch out the whole inside in incremental search for a faster version.

I might be wrong, so take what I said with a grain of salt.