Pypy has pretty bad compatibility with a lot of C extensions (numpy comes to mind), this makes a lot of larger codebases unusable on Pypy. Also Python 3 compatibility has been pretty bad.

It seems like the Mozilla grant that happened a while back ( https://news.ycombinator.com/item?id=12255586 ) has really pushed Python 3 support forward a lot.

I think we may be getting closer to Pypy having more of a prescence in the server space soon if it continues to push forward at a similar pace.

It was viewed for a long time as merely a curiosity until Armin Ringo started publishing benchmarks, and some level of CPython extension compatability was added.

I use it myself as my python runtime for some personal projects, and also to run locust.io when I need to loadtest stuff. Neither would have been practical say more than two years ago?