It all comes down to testability. In statically typed languages like C# and Java, it's very hard to test a class in isolation without abstracting hard links bet

It all comes down to testability. In statically typed languages like C# and Java, it's very hard to test a class in isolation without abstracting hard links between classes, segregating interfaces, inverting dependencies and so on. You can write "simple" systems in those languages that have the code purity you're looking for, but they won't be very testable. In the dynamic languages you mentioned, you have duck typing and testing is a walk in the park.