Why must a class implementing an interface invoke its default super methods statically?

Question

If I were to have an interface as such:

interface U {
  default void execute() {
    ...
  }
}

and a class implementing it:

class V implements U {
  @override
  void execute() {
    ...
  }
}

Why would class V's execute require U's execute to be invoked as U.super.execute() rather than super.execute()?