[lmm]

Pypy gives you at best a single-digit speedup, and requires carefully going through your dependencies and checking all your codepaths. That's rarely a good value proposition for a business - if you're growing fast enough that performance is an issue, you're going to need a bigger speedup than that pretty soon, and if you're taking the time to go through all your codepaths, it doesn't cost a lot more to make a bigger change like switching languages entirely.