Why does C++ make the element type of std::initializer_list const?

I commonly use std::initializer_list<std::string>, say {"foo"s, "bar"s}, to fill a container.

Obviously, std::initializer_list<std::string> contains temporary strings, and I can move them into a container:

#include <string>
#include <list>

using namespace std::literals;

void f(std::initializer_list<std::string> il)
{
    std::list<std::string> coll;
    for (auto&& tmp_str : il)
    {
        coll.emplace_back(std::move(tmp_str));
    }
}

int main()
{
    f({"foo"s, "bar"s});
}

However, according to cppref:

An object of type std::initializer_list is a lightweight proxy object that provides access to an array of objects of type const T.

Why does C++ make the element type of std::initializer_list const?