Why use a nested class and not the top level class when implementing a Bill Pugh Singleton? [duplicate]

The suggested implementation of a Bill Pugh singleton looks like

  // Java code for Bill Pugh Singleton Implementation
    public class GFG
    {
    
    private GFG()
    {
        // private constructor
    }
    
    // Inner class to provide instance of class
    private static class BillPughSingleton
    {
        private static final GFG INSTANCE = new GFG();
    }
    
    public static GFG getInstance()
    {
        return BillPughSingleton.INSTANCE;
    }
    }

But instead of creating a Nested static class, we can directly make the instance variable in the top class as final and static, no matter how many times we invoke getInstance, it will always return the one and only singleton object :

public class SingletonBillPughMethod {    
    
        private SingletonBillPughMethod() {
    
        }
        private  final  static SingletonBillPughMethod SINGLE = new SingletonBillPughMethod();
    
        public static SingletonBillPughMethod getInstance() {
         return SingletonBillPughMethod.SINGLE ;
        }
    
    }
class Retrieve {
    
        public static void main(String args[]) {
            System.out.println(SingletonBillPughMethod.getInstance() + "==== 1");
            System.out.println(SingletonBillPughMethod.getInstance() + "==== 2");
            System.out.println(SingletonBillPughMethod.getInstance() + "==== 3");
        }
    }

So what's the point of the nested class?