I wish I could find the video the talk where we explained this in great detail, but basically: it's hard, it's been tried and failed (notably by Armin Rigo, one

I wish I could find the video the talk where we explained this in great detail, but basically: it's hard, it's been tried and failed (notably by Armin Rigo, one of the leads of PyPy). Adding a new GC to CPython is insanely hard, and manually writing a JIT for Python even moreso.