Too many things with Pypy (and other supposedly faster implementations) don't work, so it's a no-go for a lot of projects to begin with.

In the last 10 years, I looked into pypy I think three or four times to speed things up, it didn't work even once. (I don't remember exactly what it was that didn't play nice... but I'm thinking it must have been pillow|numpy|scipy|opencv|plotting libraries).