alt Hacker Newsthe overall field is known as "gradual typing", and it is an attempt to combine some of the benefits of both static and dynamic typing (or to put it more accurately, to explore more of the benefits and tradeoffs on the static to dynamic spectrum). in the "type checkers for ruby/python/js" part of the spectrum what you are trying to ask is "how much static type safety can I add without giving up the power of the dynamic bits", so for instance you have code that generates classes as runtime (not really compatible with a strictly static type system in the most general case), but specific very common uses of code generation, like python's dataclasses, have support within the type checker.
That still has not really explained why they (those who propose that) need types in ruby specifically. Whether python has it or not is not relevant because it is another language. The argument that "language xyz has it, so ruby needs it", can be compelling, but does not necessarily have to be compelling. It needs to have a use case for ruby in and by itself. I don't see that intrinsic use case.