[evmar]

That's a really great question!

One other factor is that functional languages typically are theory first, implementation second, while non-functional languages tend to more often have the language features follow whatever the implementation admits. I know for Go they fretted a lot about how you'd efficiently compile generics, which is not something that comes up when you're designing System F or whatever.

But I believe that subtyping has a massive impact on generics, particularly in OOP languages where people expect to use lots of subtypes. There are all of these new questions around not only bounded polymorphism but also variance and mutability and how inference works.

Even TypeScript, which is following a lot of the design decisions already established by C# with the same person behind both, is still kinda just meandering around the design space and continuing to make changes to the semantics in new versions.