Why can an inner.inner class not be static?

Question

First, look at these 2 classes:
public class A1 {
public A1() {
new B1.C1();
public class B1 {
public static class C1 {
public class A2 {
public A2() {
new B2.C2();
class B2 {
public static class C2 {
Class A2 will compile just fine, but A1 will not saying that I can't define class C1 as static.
Why not?
Class C1 is not associated with an instance of B1 (because it's static), and we already have an instance of A1 (since we're in the constructor).
Why is this so radically different that A2 (which works)?

Answer 1

In class A1 the inner class B1 is just like a mehtod of class A1.
So how we cant create static variable inside a method , similarly the class A1
didnt accepting its inner class b! to create static class.
(This is my assumption/view only, may be wrong)