Sometimes generosity isn't needed. If a project (including the language it's written in) is simple* enough, casual users can add features they want for themselves.

But for complex projects those barriers will probably always be quite high.

* "Simple" is a slippery concept. I find hacking Haskell easier than hacking Python, because the type signatures and other features make it much easier to see what's going on with a minimum of investigative work. But difficulty is a big part of Haskell's reputation, and ease a big part of Python's.