I think it's a matter of numbers. There are a lot of people who use Python. (https://blog.pythonanywhere.com/67/ estimates in the low millions.) Some of them like to work on alternate implementations of Python.

I think Python is average in this respect. By comparison, here's an incomplete list of C compilers: http://en.wikipedia.org/wiki/List_of_compilers#C_compilers and you can also look at the list of Pascal compilers.