I dint know many OO languages that don’t have a useless toString on string types.

Well, that's just going to be one of those "it is what it is" things in an OO language if your base class has a toString()-equivalent. Sure, it's probably useless for a string, but if everything's an object and inherits from some top-level Object class with a toString() method, then you're going to get a toString() method in strings too. You're going to get a toString() in everything; in JS even functions have a toString() (the output of which depends on the implementation):

In a dynamically typed language, if you know that everything can be turned into a string with toString() (or the like), then you can just call that method on any value you have and not have to worry about whether it'll hurl at runtime because eg. Strings don't have a toString because it'd technically be useless.