Java method implementations whose arg types are broader than declared in the interface

What is the motivation for disallowing this in Java?

interface A {
  void foo(C arg);
}
interface B {
  void foo(D arg);
}
interface C {}
interface D extends C {}

public class E implements A, B {
  public void foo(C arg) {}
}

The compiler complains that E doesn't implement the foo(D) required by B.

I realise the underlying issue is that the following doesn't compile either:

public class F implements B {
  public void foo(C arg) {}
}

but I don't understand why Java disallows it?