Why do all code docs tools put the doc in a separate comment instead of in the code?

docs.js

// Quick idea. I love doc comments, but it's annoying that you need to repeat all of the
// argument names again, just to document them. It's easy for parameter lists to fall out
// of date. Plus, if you're using a typed language a lot of the information is already
// there. Is there a tool to parse comments like the below?

/** Create a Redux store. Using this function as a convenient example. */
function createStore(
  /** A reducer function that maps the previous state and current action to the next state. */
  reducer: ReducerFunction,
   
  /** Initial state that might come from a previous session or a server-side render. */
  preloadedState?: any,
   
  /** A function to act as a store enhancer. Use `compose` if you need multiple enhancers. */
  enhancers?: [EnhancerFunction]
) {
  // TODO: implement
}