Why the `std::function` object(i.e `fn`) still works well after the object `ins` is out of scope?

Why the std::function object(i.e fn) still works well after the object ins is out of scope? Here is the code snappit(https://godbolt.org/z/Y6KaWY):

#include <iostream>
#include <functional>

std::function<int(void)> fn;
 
 class CTest
 {
    public:
         CTest() {std::cout << "ctor:" << this << std::endl;};
         int demo(void){std::cout << "this pointer:" << this << std::endl; return 0;}
 };



 void assign(void)
 {
    CTest ins;
    fn = std::bind(&CTest::demo, &ins); 
 }

int foo()
{
     return 9;
}

 
 int main()
 {
    assign();
    CTest tes1;

    foo();
    fn();
}

The outputs: Program returned: 0 Program stdout ctor:0x7fff64960a80 ctor:0x7fff64960be0 this pointer:0x7fff64960a80 //You see, still point to the object(i.e ins) that is out of its scope