析构函数的实现问题，求指教

#include<iostream>
using namespace std;
int count=0;
class alpha
{
public:
    alpha()
    {
        count++;
        cout<<"\nNO.of object destroyde"<<count;
    }
    ~alpha()
    {
        cout<<"\nNO.of object destroyed"<<count;
    count--;
    }
};
int main()
{
    cout<<"\n\nENTER MAIN\n";
        alpha A1,A2,A3,A4;

    {
        cout<<"\n\nENTER BLOCK1\n";
        alpha A5;
    }
    {
        cout<<"\n\nENTER BLOCK2\n";
            alpha A6;
    }
    cout<<"\n\nRE-ENTER MAIN\n";
    return 0;
}
对象A1，A2，A3，A4生成后为什么不是当场销毁，而是等到A5，A6销毁后才销毁的。。。