Because it is one of the most ambitious project in opensource world and very little is known about that. It is neglected by Python Contributor community for unknown reasons ( something political it seems) . It was developed as PHD Research project by really good researchers. PyPy had written python in Pure python and surpassed performance of Python written in C by 4-20x . They delivered Python with JIT and also Static RPython : which is subset of python which compiles directly to binary. I had also personally worked together with some of the lead PyPy developers on commercial projects and they are the best developers to work together with.