ModalRoute.of(context) returns null for rootNavigator?

I wrote a simple extension to get the current route. So, final route = Navigator.of(context).currentRoute() where

extension NavigatorStateX on NavigatorState {
 Route<dynamic> currentRoute() {
    return ModalRoute.of(context);
  }
}

It works fine for a local navigator, but when I use it on a root navigator, ModalRoute.of(context) returns null. E.g.,

Navigator.of(context, rootNavigator: true).pushReplacementNamed('/home');
final route = Navigator.of(context, rootNavigator: true).currentRoute();
//    ^^^^^ route is null

Not sure why it works for a local navigator but not the root?

EDIT: I wrote a simple workaround function that fetches the current Route and works for root Navs:

Route<dynamic>? currentRoute() {
  Route<dynamic>? result;

  // Workaround (never pops, predicate always returns true)
  popUntil((route) {
    result = route;
    return true;
  });

  return result;
}

Would like something clean though.