I hope it's not literally to prevent people reinventing these simple data structures.

The ecosystem exerts a lot of pressure on developers to not reinvent fundamental things, in Haskell I practically never reach for a StrictTuple or StrictEither even when I'd like strictness specifically because they are clunkier and less well integrated with other libraries.

Scala is the only language that comes to mind with this issue (scalaz vs Cats) and my impression is that even they have mostly converged.

I would say Go has much stronger idioms than either of these languages, and wouldn't need to be afraid of people inventing their own fundamental types provided they're included in the standard library.