Why was argument dependent lookup invented?

Why was argument dependent lookup (ADL) invented? Is it just so we can write cout << stuff instead of std::operator<<(cout, stuff)? If that is the case, why wasn't ADL limited to operators instead of all functions?

Could the introduction of ADL have been prevented if C++ had had some other way to do generic output of both built-in and user-defined types, for example a type-safe printf via variadic templates?