Expound, please?

Do you mean to refer to the Global Interpreter Lock as the factor which prevents it from becoming the official path for the language? CPython, the reference implementation, has the GIL as well.

Or the PIL library (though everyone seems to use Pillow now?)

oops, I meant GIL. I work with scientific computing. In my experience, the only justification I have of using other language (mostly C++) over python is to get over the interpreter lock, which over complicates your life if you want parallelisation. Multiprocessing is just awful, specially if you work with big chunks of data (I do mostly medical imaging). PyPy, even if it's faster, still has the same GIL constraints as CPython, so not really a big advantage IMO.

We're working on it :-) In fact there are two projects - one is to just remove the GIL, one is to add STM-capabilities.