c++ ostream of object implicitly-convertible to string_view does not compile [duplicate]

I have a string-like class that is implicitly convertible to string_view. This works in almost all cases, but not for ostream inserters, where I need to explicitly write an ostream inserter for my class. Equivalent case for an object convertible to an int does work for ostream.

I am guessing the reason is that string_view (and hence the ostream inserter) are templates, but can someone explain in more detail why this fails to compile?

#include <iostream>
#include <string_view>

struct I {
    operator int() const { return 4; }
};
struct S {
    operator std::string_view() const { return "I am an S"; }
};

int main() {
    I i;
    S s;
    std::cout << i;  // Works
    std::cout << s;  // Doesn't
}

See Godbolt