[ratww]

Refactoring to use them is not really hard, as they are easily interchangeable with regular classes. They are pretty much syntax sugar for this class pattern here: https://stackoverflow.com/a/63615514

[Zababa]

That's true, but that's still a large refactoring to do, especially with going from mutability to immutability. The community might also just not like them.

[dgb23]

On the other hand in some cases this type of refactoring might actually reveal design issues with the code, maybe even bugs.