为什么C ++使std :: initializer_list的元素类型为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)); // Why ok here?
    }
}

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

However, according to cppref:

类型为std :: initializer_list的对象是轻量级代理   提供对const T类型的对象数组的访问的object。

为什么C ++使std :: initializer_list的元素类型为const？