Why does resize() cause a copy, rather than a move, of a vector's content when capacity is exceeded?

Given class X below (special member functions other than the one explicitly defined are not relevant for this experiment):

struct X
{
    X() { }
    X(int) { }
    X(X const&) { std::cout << "X(X const&)" << std::endl; }
    X(X&&) { std::cout << "X(X&&)" << std::endl; }
};

The following program creates a vector of objects of type X and resizes it so that its capacity is exceeded and reallocation is forced:

#include <iostream>
#include <vector>

int main()
{
    std::vector<X> v(5);
    v.resize(v.capacity() + 1);
}

Since class X provides a move constructor, I would expect the previous content of the vector to be moved into the new storage after reallocation. Quite surprisingly, that does not seem to be the case, and the output I get is:

X(X const&)
X(X const&)
X(X const&)
X(X const&)
X(X const&)

Why?